Crank length refers to the distance between the center of the pedal axle and the center of the crank arm, which is the part that connects the pedal to the bike's bottom bracket. This measurement is crucial because it affects the rider's pedaling efficiency, comfort, and overall cycling performance. Choosing the right crank length can depend on factors such as a rider's leg length and riding style. For instance, road cyclists may prefer shorter cranks for a higher cadence, while mountain bikers might opt for longer cranks for better torque on steep climbs.