All BMX tracks have a series of jumps built into the course. You want to get over the jumps and at the same time stay low and keep your speed intact. A lot of good mountain bikers started out riding BMX and that's where they honed their skills. Hills are divided into rollers, doubles, triples, tabletops, step jumps and six-packs. Rollers are single hills which racers speed jump.
Doubles are two single hills that the racers try to jump from the first onto the second.
Triples are three hills that a rider jumps however the hell he or she can. Tabletops are hills with flat tops. Step jumps are hills where the lip is lower than the landing. Six-packs are three sets of doubles that a rider rolls over. The turns on a BMX track are sometimes banked and sometimes flat to slow the riders down.