Copycat is a method in chess.
Let's say at the beginning of the game, your opponent moves a pawn one square ahead. Now it's your turn. If you choose to do copycat, you mirror what it looks like on the other side. You would the pawn on the same file one square ahead. Deep into the game, you should have as many pieces captured as your opponents, because if he/she captures your pawn, your able to capture that pawn
Note: You have to be the darker color in order to use this method, since the lighter color goes first.
A few people like to use the copycat method, but some say it's "illegal" in the rules of Chess.