The term ape hangers refers to a type of motorcycle handlebars often found on choppers. The primary characteristic of ape hangers is their height. The grips on that type of handlebar are usually at or above shoulder level. Ape hangers are primarily for show and actually adversely effect handling and control of the vehicle.
If you look at some large hairy biker sitting on a motorcycle with his arms rising up to grip the handlebars as if he's hanging from them, you'll see where the term comes from. It also doesn't hurt that the stereotypical biker looks somewhat ape-like even when not in the "I'm hanging from a tree" posture.