A bobber, originally called a ‘bob-job’ from the 1930s through 1990s, is a style of custom motorcycle. The typical construction includes stripping excess bodywork from a motorcycle; removing the front fender, and shortening the rear fender, which is „bobbed” (as in bob-tail), and all superfluous parts removed to reduce weight.

https://en.wikipedia.org/wiki/Bobber_(motorcycle)