A-Side vs. B-Side (A | B)
An Edit Point is where the end of one clip is placed next to the beginning of another clip on the timeline.
The A-Side of the edit is on the left side of the edit point. It is the out-point of the outgoing clip.
The B-Side of the edit is on the right side of the edit point. It is the in-point of the incoming clip.
But make sure not to confuse the A-Side and B-Side with a Clip's Head and Tail, as they are different terms.