These bikes are ones that do not require a License, Number Plate, Helmet or Insurance. They are limited to 15mph and include pedals but have a moped look to them. Some may exceed 15mph but if so, that will only be legally possible on private land.
Althought categorised as an Electric Assisted Pedal Cycle (EAPC), the default method of propulsion for these bikes is the electric motor with the pedals being used to provide momemtum to the motor or when the batteries runout. They have a throttle but only to move the bike unassisted to "walking pace" and then pedals must be used.
Contrast this to traditional EAPCs which look like push-bikes and are primarily ridden with the pedals with the motor assisting when required (Hills etc).