Wiktionary
object ball
n. (context snooker billiards English) The ball which the cue ball is intended to hit.
WordNet
object ball
n. the billiard ball first struck by the cue ball
Usage examples of "object ball".
The weather was warm and sunny, I was bringing my golf clubs down with me, and I had just discovered (and meant to put into practice) an entirely new stance which made it impossible to miss the object ball.
A jenny is a difficult in-off shot to the middle pocket, usually with the object ball close to the side-cushion.