Hub Gears:

Hub gears have a gearbox built in to the rear hub, sealed away from the elements. Gears are engaged and disengaged by a pushrod from the end of the hub. Hub gears are heavier than derailleurs, but need a lot less maintenance, and are more forgiving of misuse. They can have 3, 4, 5, 7, 8 or 14 ratios, with no overlap between them.