Let's say there's a trope for "Juggling". You realize that "Scarf Juggling" and "Knife Juggling" are common too, to the point where you can think of half a dozen examples for both. Those would be Sub-Tropes, whereas "Juggling" is generally their Super-Trope. In logic terms, "Juggling" is the genus and the different kinds of juggling are the differentia; they share the same common theme in their definition, but they each have additional features that distinguish one from another.
What makes a Sub-Trope can vary. Perhaps the most common way is that several examples of a trope have a distinctive common element unseen in the other examples. This distinctive element makes the Sub-Trope the same, but more distinctive than the broader trope. A trope can have several possible variations built in, and once examples of any of those variations are common/distinctive enough, they form a Sub-Trope. Any sub-tropes should be listed instead of the Super-Trope, because the Sub-Trope implies the Super-Trope's presence.
Compare Sister Trope.
- Alice Allusion is a basically a Shout-Out to Alice in Wonderland.
- Big, Bulky Bomb is Stuff Blowing Up when the explosive device is huge (regardless of the actual explosion).
- Black Vikings is a sub-trope of Politically Correct History and Colorblind Casting.
- Canis Major and Mega Neko are Bigger Is Better applied to canines and felines, respectively.
- Chemical Messiah is a sub-trope of Terminally Dependent Society.
- Deus ex Machina is a sub-trope of Ass Pull, where the pull is used to resolve the conflict.
- Fan Hater is a sub-trope of Hatedom, in that they hate both the work and the fans of that work. If they hate just the work, it's the latter trope.
- Hero Ball and Villain Ball are sub-tropes of Idiot Ball, just applying to actions typical of those characters.
- Heroic Resolve is a sub-trope of both Heroic Spirit and Unstoppable Rage.
- Hypnotize the Captive is literally the Distressed Damsel being Hypnotized.
- Impossibly Cool Clothes is like an Impractically Fancy Outfit, but almost strictly done in drawn media, because that kind of outfit can barely even be worn at all in Real Life.
- Jerk with a Heart of Gold and Jerk with a Heart of Jerk are both sub-tropes of Jerkass.
- Mary Sue has enough variations it's split into several types, but it's so Flame Bait-ey that none of them allow examples.
- My Hair Came Out Green is a Cosmetic Catastrophe with hair dyes.
- Our Monsters Are Different shows fantasy writers often use various and different rules to portray some of the most popular mythical creatures. Each sub-trope deals with the most common rules appearing in works involving dragons, vampires (actually, vampires get two), werewolves, ghosts...
- Parental Abandonment refers to the common device of parents who are missing or dead. Some sub-tropes are Missing Mom and Disappeared Dad, when only one parent is unavailable.
- Revolving Door Band is Revolving Door Casting applied to a musical group.
- Something Else Also Rises is a form of Does This Remind You of Anything?, where the "anything" is... male... "excitement".
- Too Incompetent to Operate a Blanket is a variation of Strawman Product, in that the strawman aspect is making a product look far harder to use than it actually is.
- What Measure Is a Non-Cute? points out the recurring portrayal of cute animals as the good guys and non-cute animals as the bad guys. Reptiles Are Abhorrent is a sub-trope of this, as it points out reptiles are almost always portrayed as evil and vicious.