A "Swap" is where you create a card or project to share with others. It usually has restrictions, like using current Stampin' Up! product, and sometimes a theme. You then re-create the project the same number of times as there are people in the swap. The person who is hosting the swap collects everyone's creations and then returns one of everyone's creations to you.
For example:
There are 20 people in a swap I have joined. I make 20 cards (all the same) and post them to the person hosting the swap. The host collates and shares out all the swaps, and I get back 20 different projects including one of my own.
Swaps is a common way for Stampin' Up! Demonstrators to share ideas. If you want to join in and be a part of the Stampin' Up! community...