What is the meaning of Eight-ball?

A pocket billiards (pool) game played with sixteen balls (a cue ball and fifteen object balls) on a pool table with six pockets.

The billiard ball, almost always black, bearing the number eight.

A portion of cocaine or methamphetamine weighing 8 of an ounce, or 3.5 grams.

A black person.

A spherical attitude indicator.

To outplay (an opponent) by potting all one's color balls and then the black (or eight-ball) without the opponent potting a single one.

Source: wiktionary.org