Some tropes can be pretty broad. Some can be so broad that even a specific form of them can be tropes by themselves.
Let's say there was a trope for 'Juggling'. You realize that "Scarf Juggling" and "Knife Juggling" are pretty common as well, to the point where you can think of half a dozen examples for both. Those would be Sub-Tropes, while "Juggling" in general is their Super-Trope. In logic terms, "Juggling" is the genus, while 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 common element not seen in the other examples. That makes them distinct from the larger trope, while still being included. Or, as mentioned above, a trope can have several possible variations built in, and once examples of any of those variations are common enough, they form a sub-trope.
Heck, some tropes can be sub tropes of more than one super trope. This can be a shared aspect of them or actually combining the two tropes.
Compare Sister Trope.
- Hero Ball and Villain Ball are sub tropes of Idiot Ball, just applying to actions typical of those characters.
- Mary Sue has enough variations that it's split into several types.
- Our Monsters Are Different shows that fantasy writers often use various and different rules to portray some of the most popular mythical creatures. Each subtrope deals with the most common rules that appear 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 subtropes are Missing Mom and Disappeared Dad, when only one parent is unavailable.
- What Measure Is a Non-Cute? points out the recurring protrayal of cute animals as the good guys and non-cute animals as the bad guys. Reptiles Are Abhorrent is a subtrope of this, as it points out that reptiles are almost always protrayed as evil and vicious.
- Deus Ex Machina is a sub trope of Ass Pull, where the pull is used to resolve the conflict.
- Impossibly Cool Clothes is like an Impractically Fancy Outfit, but almost strictly done in drawn media, because that kind outfit can barely even be worn at all in real life.
- 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.
- 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.
- Heroic Resolve is a sub trope of both Heroic Spirit and Unstoppable Rage.
- Princess Classic is a form of Everything's Better with Princesses, but about a specific princess archetype.
- Hypnotize the Princess is literally the Damsel in Distress being Hypnotized.
- Big Bulky Bomb is Stuff Blowing Up, but that the explosive device be really big (regardless of the actual explosion).
- Canis Major and Mega Neko are Bigger Is Better applied to canines and felines respectively.
- Something Else Also Rises is a form of Does This Remind You of Anything?, where the "anything" is... male... "excitement".