What does it mean to swap tiles in scrabble?

Swapping tiles is an option that you have each turn in Scrabble. Instead of making a Word, you can choose letters in your hand that you don't want, and trade them for mystery tiles that are still available. Of course, you won't get any points that way, and so making a low-scoring Word that gets rid of some of your unwanted tiles is sometimes a better option. If you can't make any Words though, then swapping is the best choice.