A group of similar cars or trucks. Some classes might include:

Rookie stock (inexperienced racers with stock 27T motors)
19 turn expert (professionals with modified 19T motors)
Sportsman nitro (intermediate nitro cars)
Factory modified (factory team racers with any modified motor)
Open stadium truck nitro (nitro stadium trucks with any engine)
Team Losi XXX-T (only Team Losi XXX-T's run in this class)