Mate, to put it simply. It is the lenth of the bike. Take the adamant a3, spec: Wheelbase: Short 1005mm, Long 1030mm Chainstay Length: 362mm BB Rise: Short 60mm, Long 55mm Head Angle: 72 degrees Centre of BB shell to top centre of head tube: Short 595mm (23.5"), Long 610mm (24") The longer the frame, the more leverage you will get for gaps etc. A short frame would be nice and flicky (good for sidehops, frenchies and comptitions.) Also a common thing people look for is the BB RISE. This is like how high the bottom bracket is. Low; (im not really sure the pro's or cons for low bb's) But high BB rise; the bike would stay on the rear wheel alot nice (alot less hopping). And just generally makes the bike ride nice. EDIT: Btw it's not a nooby question!