Catering for different processor speeds in a game

I've got a fun and simple little pong game going, but after running it on a friend's computer, I suddenly noticed a MAJOR hitch. It runs at completely different speeds depending on the processor speed of the computer. I need to stop this, so that the game will run at the same default speed regardless of the processor speed.

Someone mentioned "tick limiting", but I'm not sure how to implement that (google was little help, all I got was that phrase, and the idea that it's something to do with the processor cycles and the clock?).