object ball
noun
ob·ject ball 
ˈäb-jik(t)-,
-(ˌ)jek(t)- : the ball first struck by the cue ball in pool or billiards
also : a ball hit by the cue ball
Example Sentences
Recent Examples on the Web These are played on a pocketless table with three balls — two cue balls and one object ball. 
John Torsiello, courant.com, 13 Nov. 2019 When a sliding cue ball makes contact with an object ball, the two will always separate at an angle of 90 degrees. Popular Mechanics, 5 Jan. 2018
John Torsiello, courant.com, 13 Nov. 2019 When a sliding cue ball makes contact with an object ball, the two will always separate at an angle of 90 degrees. Popular Mechanics, 5 Jan. 2018 Word History
First Known Use
1856, in the meaning defined above