A chopper is a type of custom motorcycle which emerged in the US state of California in the late 1950s. A chopper employs modified steering angles and lengthened forks for a stretched-out appearance. They can be built from an original motorcycle which is modified ("chopped") or built from scratch. Some of the characteristic features of choppers are long front ends with extended forks often coupled with an increased rake angle, hardtail frames, very tall "ape hanger" or very short "drag" handlebars, lengthened or stretched frames, and larger than stock front wheel. To be considered a chopper a motorcycle frame must be cut and welded at some point. I.e. the name chopper. The "sissy bar", a set of tubes that connect the rear fender with the frame, and which are often extended several feet high, is a signature feature on many choppers.

A custom motorcycle is a motorcycle with stylistic and/or structural changes to the 'standard' mass-produced machine offered by major manufacturers. Custom motorcycles might be unique, or built in limited quantities. While individual motorcyclists have altered the appearance of their machines since the first days of motorcycling, the first individualized motorcycles specifically labeled 'Custom' appeared in the late 1950s, around the same time as the term was applied to custom cars.