Definition: A game with no open frames.
By official USBC rule, a clean game is a game in which a bowler records a mark in every frame. That is, assuming you mark in each of the first nine frames, you can strike on your first shot in the 10th and throw two gutter balls (an extreme example) and still be credited with a clean game. Likewise, you can spare in the 10th and not strike on your fill ball and be credited with a clean game.
Also Known As: Patch
Examples: With all these strikes and spares, I'm on my way to a clean game.