Forget it, I found this. Add to it if you like, still a little confusing.
There is a common misconception that frame traps leave you at frame advantage and then doing another move that has a startup less than that frame advantage. This is a link, and if the frame advantage is still greater than the startup when the opponent is blocking, then that is a block string.
A frame trap is a sequence of moves where the first move's frame advantage (or disadvantage) plus the startup frames (not counting the first active frame) for the follow-up move creates a window (the frame trap) where the opponent, even if they perform a move to react, will be stuffed (or even counterhit) because the active frames of their move will not come out before the active frames of the second move of the frame trap.
Of course, this means that frame traps are opponent-dependent; not all frame traps will work on all characters, and there are certain situations where you might not have any frame traps because an opponent has a certain move which will always allow them to escape the frame trap.
