What does it mean to roll a clean game in bowling?

Answer 1

A "clean game" in Bowling is simply a game that has no opens. That means that every frame, the two shots equal 10 pins.

A mark is either a strike (10 pins in one shot) or a spare (ten pins in two shots). So a clean game would also be a game in which a bowler marks every game.

Note: Some bowlers do not consider it an "open" (frame does not equal 10 pins) if the first shot resulted in a "split."

Answer 2

each frame bowled in a game either was a strike or a spare was converted on the second ball.