In the Super Smash Bros. series, "gimping" is the practice of stopping an opponent from recovering back to the stage, usually by grabbing the ledge before them or just going out and hitting them. However, I'm curious... where did the term actually come from? Was it named after a player who practiced it, similar to planking? Or is it something else entirely?
The term 'gimp' is a sometimes-derogatory term for one who is crippled; a gimp. When a player uses the techniques you've described, they're effectively crippling their opponent, by removing their ability to recover. In the same vein, it could also be related to the fact that in this scenario, the player trying to make the recovery has a 'handicap' (or is crippled) when compared to the other player, who is effectively in control of the situation.
In this particular context, the removal of the recovering player's ability to grab the edge is the 'gimp'.
In both of these variances, the player is control is able to use certain techniques as a means of 'crippling', or 'gimping' their opponent.
This is all absolutely speculation, but it didn't feel right as a comment.