A character goes back to the past. From the other character's point of view, they seem to say, do and know things that imply a frighteningly accurate knowledge of the future. Of course, they do not need special powers to be able to do this — they only need to remember, because they have already lived though it before. If their chosen method of time travel is easily accessible, they can even try to "save-scum" their lives so that it follows an ideal path.
A variation is a character who is Trapped in the Past before their actual date of birth, but in a period that they are familiar with from history books.
Note that you should not even attempt this without significant historical research under your belt, and even then, people have messed around with historical dates so often during the times and truth intermingled with myth so much that it will probably not do you a lot of good anyway. (We would also mention things like the language barrier, but those belong to the main Time Travel trope.)
Not to be confused with "retroactive clairvoyance", an entirely different term that has been used for the act of retrofitting vague predictions to events that have already happened.
If the character relies on science and engineering from the future, rather than knowledge of the current time period, they are Giving Radio to the Romans. Often overlaps with the "Groundhog Day" Loop in those cases where the character is actually aware they're reliving the same day over and over again.
Warning, spoilers below.
- Layla Miller of X-Factor knows stuff because a version of herself traveled eighty years into the future and learned stuff and then told her past self.
- In modern age comics Barry Allen and many of his family member know the future, at least in vague terms, due to spending so much time in the 31st century. Barry himself was able to make use of this knowledge even after his death by time traveling to important events while he was still alive.
- In Memento Vivere, a Final Fantasy X fanfiction, Rikku helps Braska's group figure out how to get through Bevelle’s Cloister of Trials.
- Doctor Strange in Child of the Storm does this all the time, to the point where it's impossible to figure out how much of his foreknowledge is due to this and how much to actual precognition. This trope, combined with total mastery of the Batman Gambit, lets him basically run the plot from, until the finale of Book I, mostly offscreen.
- In Lest Darkness Fall, 1930s archaeologist Martin Padway is mysteriously transported to 6th Century Italy (where the "Dark Ages" are about to come down with a vengeance). He is able to use his knowledge of classical history to pull this off a good deal.
- In Time Enough for Love, this is how archprotagonist Lazarus Long hopes to survive and prosper in the 1920's United States, since that's when he grew up and he has extensive period and personal knowledge of the era. Two things foil him: first, he arrives too early due to a miscalculation and winds up in 1916, on the cusp of U.S. involvement in World War I. Second, he falls in love with his mother Maureen and, in a misguided attempt to impress her, enlists in the army. However, he does entrust to Maureen a wealth of information on the future history of the United States in that timeline, allowing her to quietly abet several key events that help things turn out the way they should.
- Time Scout's scouts and guides really want to take advantage of this. They want to see and observe important historical events first hand. In the series, the only time it's deliberately taken advantage of is by the Ripper Watch Team, finally learning who Jack the Ripper was.
- In Warrior Cats, a bunch of characters are shocked when the time-traveling main character tells them where humans will build a barn and that off in the mountains there's a place they can live. Turns out that he's just speaking from his own experiences; he's far in the past.
- This is the Twist Ending to Scenes From An Alternate Universe Where The Beatles Accepted Lorne Micheal's Generous Offer. Ringo managed to go back in time and tell his past self what to do in order to bring the Beatles back together. It ends with the new Ringo doing it again, in order to make an even better universe.
- The Magic Treehouse book Civil War on Sunday has a minor example in Jack telling a wounded soldier that someday the war will end and so will slavery. The soldier then asks him if he can see the future, to which Jack replies "In a way."
- On Babylon 5 all the various Minbari prophecies were actually made by Sinclair, who traveled into the past and became Valen. The prophecies simply predict what he knew would transpire in the future.
- Doctor Who, both old and new, does this all the time. In particular, the Third Doctor frequently remarked on how "primitive" Earth technology was during his exile in the 1970s.
- Although it's debatable whether this is by comparison to humanity's future or to his native Gallifrey (which would make this more a case of Cultural Posturing).
- Quantum Leap invokes this trope on occasion. For example, once Sam made a bet that Gerald Ford would trip going down the stairs out of Air Force One, which, of course, then happens.
- Lost Season 5 did this a lot once the Time-Travel started.
- In Outlander and the books on which it was based, Claire time travels from 1945 to 1743. She arrives in 1743 with some historical knowledge about how the Jacobite Risings are going to play out. She's not a Scottish history expert, but she knows that an English victory is a Foregone Conclusion and that the Final Battle Of Culloden is three years away in 1746. Because of this knowledge, she can tell certain other characters things that are going to happen.
- In Star Trek: Deep Space Nine, there's seldom actual time travel involved but the various Bajoran prophecies were made by ancient Bajoran clerics who received visions of the future from the Prophets, who exist outside of time so it's much of a muchness to them. Presumably, they received these visions during orb experiences. For instance, Trakor's First Prophecy states that the Emissary will find the Celestial Temple and the Prophets will gave him his life back. This happens thousands of years later, in 2369 as depicted in the pilot "Emissary", when Sisko discovers the wormhole. His encounter with the Prophets helps him to realise that it is time to stop living in the past and get on with his life. Consequently, Prophecies Are Always Right though they're usually rather vague and there is the occasional Prophetic Fallacy and/or Prophecy Twist during the series.
- In Chrono Trigger, Magus ends up in the past (ironically, coexisting with himself when he was a young boy named Janus), and uses his knowledge of the future (which he experienced as a young boy) to gain himself the position of a prophet in the royal palace.
- A key gameplay mechanic in Radiant Historia, where the protagonist has the ability to jump to certain times and places in his life in order to Set Right What Once Went Wrong. Gets a double-dose because there are two timelines which are linked together, so progress in one provides hints as to events that may occur in the other.
- A "Groundhog Day" Loop version of this happens in The Legend of Zelda: Majora's Mask. Learning where everyone in Termina is going to be during the three days you're in Termina is crucial to some of the sidequests.
- Undertale Lampshades this. After the first playthrough of the game, some characters will occasionally make comments that the player character seems to usually know what's about to happen, as though they've seen it all before.
- Archer in Fate/stay night knows all about Shirou's abilities, how he will injure himself with projection, the identities of Heroic Spirits who haven't revealed themselves, Saber's backstory, what the Grail really is, etc. Hint: He's Shirou from the future, so he not only lived through what is basically the Fate path, he's also had time to research on people he saw then like Caster and then correctly identify her as Medea. He also knows lots about the Big Bads' plots before they implement them and whatnot.
- Akane's attempts to use this trope to alter the timeline form the main plot of Nine Hours, Nine Persons, Nine Doors.
- Repeated in the sequel, Virtue's Last Reward... well, kinda. The purpose of the second Nonary Game was Akane teaching Zero how to alter the past using Mind Swap on his younger self, so that his younger self would get the experience necessary to survive another Nonary Game which he would've been a part of had he not swapped minds with his older self, who would know how to survive the Decision Game in Zero Time Dilemma, thereby preventing the release of Radical-6.
- The time-traveling Cassie Wells of Times Like This has used warnings from her future self to stay away from bad mistakes ... such as knowing ahead of time which men in a bar are safe to cruise, and which are married, potential date-rapists, or otherwise trouble. She deliberately avoids telling herself who she will fall in love with for good, afraid that if she knows, she'll screw it up. And the fact that no one has shown up from the future to tell her, suggests that her willpower is fairly strong on this point.
- Kevyn Andreyasn in Schlock Mercenary travels back in time with a database of news reports and other information, after saving the galaxy he uses lottery numbers to make a lot of money (which ends up getting him in trouble with The Mafia). The version of Kevyn from the past uses stock market information from the same database to also make a lot of money (which mostly gets spent saving Tagon).
- Red vs. Blue: Wyoming uses his time distortion unit to keep looping time whenever he gets beaten by Tex and the Blues, allowing him to foresee several of their plans (for example, he knows where Tex is hiding with her invisibility unit, and knocks her out). However, thanks to a special ability of his Laser Blade, Tucker has Ripple Effect-Proof Memory, and uses this trope to his advantage to kill Wyoming and save Caboose's life.