A bobber is a lean, mean, stripped-down motorcycle. The owners take off anything they consider unnecessary, usually including the front fender and part of the rear fender, along with anything that adds weight without doing much work.
Bobbers are lightweight motorcycles for this reason and run light and fast, maximising power by minimising drag and drain. A bobber isn't a chopper because the frame remains standard, but it's close. Ride light and fast on a bobber.