Downhill racing is a true test of nerve, and one's ability to control their bike under extreme conditions. The concept is to get down the mountain as fast as possible. Downhill courses usually contain a succession of big jumps and drops over rocks, trees and other obstacles. The ride is all about controlling your bike at high speeds- breaking... cornering... riding to the edge of one's ability.
Downhill apparel is all about protection... "body armor".
Bikes used to race downhill have large platform pedals. The clipless versions of downhill platform pedals are similar to a mountain bike clipless pedal, except the platform shaped exterior has a much larger pedal area and is designed to allow your feet come on and off the pedals easier while planting turns.