Sport lead climbing relies on fixed bolts for protection along a predefined route. The lead climber ascends the route with the rope tied to his or her harness and clips into each bolt or quickdraw to protect against a fall.
The biggest distinction between bouldering and other types of climbing is that, in bouldering, there is no use of a rope or harness. Instead of relying on ropes for protection, bouldering usually relies on crash pads (thick padded mats) to protect climbers when they fall. Additionally, routes (called “problems” in bouldering) are not typically more than 20 feet tall. Having a partner isn't strictly necessary, but spotting is an important skill for bouldering.
Trad (short for traditional) climbing is a style of outdoor rock climbing where the lead climber places removable protection along the route in order to protect from falls. The protection is then removed from the route as the team’s final climber ascends.