“Swapping” usually refers to some form of partner-sharing, where two couples will engage in either a hard swap (also called a full swap), or a soft swap.
Hard Swap / Full Swap
This refers to the act of fully exchanging partners in the same room, where individuals will most commonly engage in penetrative sex.
Soft Swap
The difference for a soft swap is that activities are much more limited - usually to kissing and touching, and no actual sex.