Take a bike (motorcycle) and 'chop' off everything not necessary for moving down the road. This started after WWII with G.I.s taking surplus bikes like Harleys, Triumphs, and Indians and removing the military gear attachments for comfort and speed. By the late fifties, choppers started refering to customized bikes that reached their peak in the late 60's/early 70's. A raked fork angle with extended forks, lowerd bike and a bitchen' paint scheme are all hallmarks of this type of bike.