Any skill or ability that only a select few know how to/can use, from magic to martial arts to metallurgy techniques. Even the art itself might be unknown to the world at large, but the crux of the trope is that the know-how to use it is limited to a relatively isolated group or person. Some Secret Arts aren't even particularly jealously guarded and only remain secret via their sheer obscurity.
Sometimes the technique is similar to Lost Technology being a Supernatural Martial Arts techniques, magical spells or just bread-making techniques that were invented eons ago but have been lost/buried/forgotten/not quite destroyed for a variety of reasons.
Perhaps their civilization collapsed or these techniques were simply were too powerful and/or dangerous and needed to be sealed away; the point is, no one has seen and/or heard about them in a very long time. They will always, however, be superior to their modern counterpart, which will often make them the subject of a lengthy search quest by heroes or villains to further the plot.
Usually, one of the benefits of joining The Order. Can be (or encompass) the Dangerous Forbidden Technique. The Dark Arts are often this due to being outlawed. Often taught by a type I or III Obsolete Mentor.
Often overlaps with Signature Move (especially where Video Games are concerned), with the difference being that a Signature Move is the one the character is best known for using (secret or otherwise), while a Secret Art is the one that only they know how to use in the first place.
- Triangle Heart 3: The Fuwa-ryuu sword style, exclusive to the Takamachi family.
- Naruto has a few forbidden Jutsu sealed away in scrolls kept heavily guarded due to them being either Dangerous Forbidden Techniques or The Dark Arts. The series also has Secret Jutsu, which are usually carefully guarded techniques passed down a clan as part of their Theme Deck.
- Kirigakure has a strict secrecy policy regarding the abilities of the previous Mizukage. By the time of the Fourth Great Shinobi War, the shinobi from Kirigakure are only familiar with the jutsus of the Fifth Mizukage. The resurrected Second Mizukage realizes how their policy backfired because nobody from his village knows how to fight against his own jutsus, regretting that he didn't left more legends about him behind.
- Fist of the North Star has a number of examples:
- Hokuto Shinken, a martial art that results in the instant death of the opponent, is known only to Kenshiro, Raoh, Toki and Jagi. This is actually enforced by the practitioners of the style, as Hokuto Shinken is only allowed to have one successor, and those who aren't chosen can either stop using it or be made unable to use it (by death, destruction of their arts or memory wipe depending on what the successor decides).
- Hokuto Ryuken, Hokuto Shinken's sister art, is known only to one master and his three apprentices.
- Nanto Seiken has 108 styles, each with a master and (theorically) a small number of minor practitioners. The strongest style enforces it, as there can be only a successor and an apprentice who has to kill his master to succeed him.
- Gento Kou Ken has only three (five in the anime) known practitioners.
- There is a fighting style known as "Rokushiki" in One Piece that utilizes six techniques. The members of CP9 were practitioners of this style. There are a couple of high-ranking Marine officers that can use some of them, as well. But, this trope truly comes into play in the case of CP9's Rob Lucci, who knows a hidden seventh technique known as Rokuougan. Only those who have completely mastered the six other techniques can learn it.
- In Fairy Tail, the dragon slayers all have Secret Arts: for example Natsu's "Crimson Lotus: Exploding Flame Blade", Gajeel's "Karma Demon: Iron God Sword", or Wendy's "Shattering Light: Sky Drill".
- In Slayers, cooking dragon meat is a secret art, and you have to endure a harsh apprenticeship from an Old Master to learn how to do it. It turns out it's incredibly difficult to catch dragons and slay them with kitchen implements, and it's even harder (and incredibly time-consuming) to cook their meat properly and remove all poison from it.
- In Fullmetal Alchemist, Mustang's flame alchemy is shown to be this in a flashback sequence, with the formula for it being tattooed onto the back of a flame alchemist's chosen second (in Mustang's case, it's Hawkeye) and never written down so that only the rightful heir to flame alchemy can ever learn it. It's a good thing, considering how enormously destructive flame alchemy is demonstrated to be throughout the series.
- Lady Shiva knows several martial arts skills that no one else knows due to her killing the last master of the practice, and her signature move is the "Leopard's Blow" is also used only by her.
- Robin Series: Tim is the last student of an ancient holistic Tibetan martial art which then dies out in its complete form along with it's last master as Tim never completed his training and the master's longest lasting student was only interested in select parts of the fighting aspects of it, rather than the meditation and healing aspects.
- Star Wars: The Force, though the Star Wars Expanded Universe and Legends show that the Jedi Order doesn't have quite as strict a monopoly on Force abilities as they'd perhaps like.
- Five Point Palm Exploding Heart Technique from Kill Bill, which even Bill was surprised was taught to someone else by Pai Mei.
- In A Brother's Price, the so-called "Paths of Pleasure" is treated as this. Jerin is asked whether his grandfather passed it on to him. It is, essentially, the art of keeping all wives happy in a polygynous marriage. Jerin is very embarrassed when asked about it, he doesn't think it should be discussed in public.
- The Destroyer: Sinanju. Only two people in the world know it.
- Within the first hundred or so books or so (literally; its a long series), we've run across a few others. In the history of the Korean village the art's home to, there have been a few rogue students and at least one second son who received surreptitious training and chose self-exile. In fact, Sinanju actually turns out to be in Remo's genetic heritage... but still, it's a pretty well-kept secret and there are probably at most three masters of it alive at any given time.
- Discworld's Lu-Tze. Deja fu. Of course the monks don't know it, he hasn't taught them!
- Earth's Children: The Sharamudoi people have a secret technique for making chamois skin very soft and pliable, and only members of their cave are allowed to know it. This is done for economic reasons—soft chamois is a valuable commodity and other tribes trade things they want for it.
- In the Young Wizards series, every entity in existence (people, planets, universes, etc) has a "kernel", a wadded-up line of symbols from the Language of Magic which both describes and is the laws by which that entity operates. Since letting any random wizard who felt like it alter a planet's kernel would be a Bad Idea, the knowledge and training of how to manipulate kernels is provided on a strict need-to-know basis. On any given planet populated by sentient beings, there's probably only one or two wizards who can do kernel manipulation.
- In An Instinct for War's story A Sword is Drawn, the emperor gives a story how sword manufacture used to be known by a few who kept their methods secret. As it turned out, these "sword masters" knew their art as a ritual than a craft. If they missed one step, the swords turned into abominations and no one knew why. When the art of swordmaking was finally known, it was realized that there was nothing special about the art—anyone could make them. More and better swords were able to be made. The emperor uses this story to support his point that a disgraced general is not a craftsman of war, but an unimaginative follower to the principles of war.
- Coiling Dragon: The Straight Chisel School of stonesculpting allows Earth-style magi to use their sense of stone to carve without the use of precision tools. Doehring Cowart developed it during his life, but Linley is the only person to have learned it.
- Journey to Chaos: Magic has a lot of these.
- In A Mage's Power, Dengel teaches Eric a tracking spell that cannot be blocked or obstructed by any means. This makes Eric the first person to ever learn it because it is Awesome, but Impractical. Dengel never bothered to name it because he knew no one he taught in his previous life time would ever use it.
- In Looming Shadow, Grey Dengel teaches Eric "Mana Conversion" which enables him to dissolve physical matter into mana for use in spells. No one else knows this because it is an Enlightenment Superpower that few can achieve with their sanity in tact.
- The Lost Fleet has a non-supernatural example in the form of most advanced Space Navy formation tactics, which has become a lost art by the start of the series proper for the equally mundane reason that getting really good at it takes hundreds of hours of intensive training. As the Alliance-Syndicate Worlds war deteriorated into an increasingly bloody stalemate and casualties mounted, the less time there was to train new officers to replace those who fell in battle and the more abbreviated their training became, a vicious cycle that ultimately led to the two opposing sides launching barely-trained crews in poorly-built ships into wasteful headlong charges... Until recently-defrosted Human Popsicle Captain John Geary, who enlisted in peacetime and had the benefit of a full-length Academy syllabus and several large-scale fleet exercises, ends up in command of the titular Lost Fleet.
- This extends to the entire field of mechanics in Warhammer 40,000, where basic repair procedures are turned into complex rituals (burning incense before oiling a gear, for example). The techpriests get mighty miffed when people get stuff working without their assistance.
- Dragon Age: The Templar's anti-magic abilities are exclusive to them among the Ferelden warriors. Also, Blood Magic.
- The golem-making.
- The Elder Scrolls
- Necromancy tends to become this in times and places when it is illegal. Practitioners must meet in secret to share knowledge and related paraphernalia.
- In Skyrim, Big Bad Alduin has several Thu'um shouts unique to him. SLEN TIID VO, the shout he uses to revive dead dragons, is exclusive to him. His Meteor Storm shout is also one (though "Storm Call" is very similar in function and is obtainable). Another is "VEN MUL RIIK", "Wind Strong Gale", which shrouds an area in thick concealing mist.
- The "Enigmatic Engineering" perk in Stellaris makes it impossible for anyone to reverse-engineer your technology. Making any unique technologies you've gained through special events like Dragonscale Armor or Psi-warp drives this.
- Street Fighter: The Ansatsuken fighting style
- In The Legend of Zelda: Twilight Princess (and possibly other Zelda games), Wolf Link can find a golden wolf spirit, which is actually an ancient warrior, who teaches him various forgotten sword techniques which greatly boost his effectiveness.
- Somewhat toyed with concerning the Early Summer Rain Jab in the last case of Ace Attorney Investigations. After Larry's blunder with the Samurai Spear, the studio puts a gag order on the incident and tries to pretend the move doesn't exist. Kay comments that it seems like a lost art because of that.
- In The Legend of Spyro the Old Ways of dragon combat, particularly the Fury Wave attack, fall under the almost lost/destroyed category. It's implied that only the Elder dragons can teach the techniques, and there just aren't many Elder dragons (or any other dragons for that matter) left due to a years-long war
- Many Pokémon, mostly Legendaries, have an attack only that specific Pokémon (and its family, if it has one) can use under normal circumstances. Bulbapedia lists the article as "Signature Move", but it's not to be confused with the trope Signature Move.
- Additionally, only the starter Pokémon can learn the elemental Pledge moves, and only their final forms can be taught the strongest Grass/Fire/Water moves (Frenzy Plant, Blast Burn, Hydro Cannon). Draco Meteor can only be taught to Dragon-types with a high enough friendship.
- Pokémon X and Y introduces Mega Evolution, which fits this trope for both Pokémon and trainers. It is a temporary boost in power only available to certain Pokémon, and then only if they are holding their species' specific Mega Stone (meaning they can't hold any other item), and their trainer has a Mega Ring to activate the transformation, which only a select few trainers have (including the Player Character, after reaching a certain point in the game).
- Pokémon Sun and Moon adds Z-Moves, which allow a Pokémon to perform a stronger-than-normal attack once per battle. Most Z-Moves aren't covered by this trope, as can be used by any Pokémon with a regular move of the same type, but some can only be used by certain Pokémon, such as Pikachu's Catastropika.
- Enforced in the Orre games with the various Shadow moves. As the moves run off of the Pokemon's Shadow power, they are immediately abandoned and replaced with more normal moves once the Pokemon is purified. Operating words: "more normal", since one of those moves is available to the user through purification and through no other method, like Lugia learning Deoxys' signature move Psycho Boost.
- M.U.G.E.N: Kung Fu Man, the "template" character that comes with the game engine, has the "Kung Fu Palm" attack as this, according to one of his winquotes:
"Your moves are too predictable. You want to learn Kung Fu Palm? It's not for novices."
- In Fate/stay night, Souichirou Kuzuki is a master at a secret assassination martial art only referred to as "Snake". The art focuses on using misdirection and hooked movements that are actually more effective the more well-trained the opponent is in traditional martial arts, as they rely on fooling the fighter's training and exploiting holes in their defenses. However, the art's real effectiveness is in the element of surprise and catching the victim off-guard: once a skilled fighter realizes the nature of the art, they can adjust to match it, and then the Snake practitioner is at a severe disadvantage.
- In The Order of the Stick, the Spellsplinter Maneuver is well-known enough amongst fighters and swordsmen that it can be recognized on sight, but the only person alive who knows how to execute the technique is Roy Greenhilt, who learned the technique from his grandfather while he was spending time in the afterlife.
- Yu-Gi-Oh! The Abridged Series' explanation for why nobody could summon Exodia until Yami did: "This game makes no sense and nobody could figure out how to do it!"
- Avatar: The Last Airbender: In need of gaining firebending Aang and Zuko travel to the city of the first firebenders and discover ancient dragons who teach them an ancient form of firebending (or at least the philosophical underpinnings of it; fire as life and energy, rather than simply rage and destruction). There are also some more specialized examples:
- Lightning-bending, the ability of a few high-end Firebenders to, well, blast people with lightning. In the original series, only Ozai and his daughter Azula know how to do this; by the time of the sequel series, the ability appears to be commonplace. Iroh develops his own counter to this: a lightning-redirecting ability, which he teaches to Zuko, who later teaches it to Aang.
- Chi-Blocking, a pressure-points sort of technique that temporarily disables your opponent's bending powers. Only Ty Lee can do this at first; but, since it doesn't require inherited magicalness, this skill is also relatively common in the sequel, making it much more feasible for non-benders to fight benders.
- Bloodbending, an evil version of Waterbending that allows you to control your opponent's body—making them helpless, since all the magic powers in their world are Supernatural Martial Arts. It was invented by an imprisoned waterbender who had nothing available to bend but the blood of her captors. Katara learns it from her, but is reluctant to use it. This one is still rare in the sequel, but nonetheless important, since Amon combines it with Chi-Blocking to permanently disable people's bending.
- Martial Arts: Many forms, such an Ninjitsu, were traditionally taught in secret by a very few masters. The fact that they were explicitly forbidden and/or illegal forced them to remain underground. Sometimes prospective students were bound by an oath of silence, especially when this was a weapon of rebels. These days, though, secret techniques don't remain secret for very long.
- Some techniques were developed by particular martial artists, who died without passing them on. But those arts are not so much Secret as they are Forgotten.
- Liechtenauer's school of German swordsmanship. In its time it was very exclusive, and it became entirely lost at some point in the 18th century. It's been brought back from the dead thanks to the finding of a handful of Medieval and Renaissance combat manuals, but it remains highly obscure.
- In particular, the five Meisterhau or Master-hews in said style, originally known as the "Secret-hews" of said style. They were designed to regain the initiative in a fight by attacking and defending in one motion. Obviously, they would later become much more widely known and drop the original "Secret" name.
- In Vajrayana Buddhism and presumably many other religions, certain teachings are only passed down from master to student.
- One of the major draws of esoteric traditions (including esoteric sects in mainstream religions) is the assumption that they are unknown because most Puny Humans can't handle them.
- In the old days it was stage magic. In the 1800s, it was much harder to learn how to do magic even if would-be magicians were serious about learning because other magicians were so reluctant to teach newbies back then. Nowadays, there are hundreds of books available for learning the art—but even today it's still frowned upon by most magicians to reveal a secret to a layperson. Also, if one wishes to join a group such as the The Magic Castle or The Magic Circle, one usually has to prove that they're at least somewhat competent with magic by demonstrating decent ability and take an oath swearing that they will never reveal magic secrets to anyone not serious about learning the art—failure to follow this oath can get you banned from most groups.