Bones0
Smash Legend
There's obviously no official definition of a frame trap, but it can apply to pretty much any situation in which a player intentionally conceals his frame advantage in order to set a trap for his opponent. Your goal is usually to make the opponent THINK they can punish you when they actually can't (or can, but requires them to be nearly perfect).
A common example of a frame trap in Melee is what Mew2King does with Marth in neutral. Often, he will do an autocancel nair spaced far away from the opponent. The opponent sees the aerial and tries to punish the landing lag by running in with a grab, but when nair is autocanceled, it has a deceptively small amount of lag. This allows M2K to dash back, avoid the grab, then dashdance back in and get a punish. You can ofc do frame traps by timing your attacks on shields or even by dodging in a certain way, but the video was totally wrong because it was mostly concerned with spacing attacks which has nothing to do with frame advantage (unless the increased space was the reason for the frame advantage, which it wasn't in the examples).