Usually used in the gym when you're trying to convince someone to do more reps. Can also be used in other situations when you are trying to make someone do something.

He had big balls to try that stunt.

A song from the band AC/DC.

What Stephen Colbert has that enables him to speak the truth about the Bush White House and the White House Corespondents.

when something is a pain in the ass, it's "big balls". italian-american slang.

In the game of pool, the big balls are the stripes, as opposed to the solids, which are called small balls. One can imagine that the solid-colored balls look smaller than the stripes, although they are all identical except in appearance.

Balls that are big