What is the difference between single-sided and double-sided timing belts?

What is the difference between single-sided and double-sided timing belts?

Single-Sided Belts: Have teeth on one side only, used for standard, unidirectional power transmission.
Double-Sided Belts (DA/DB type): Have teeth on both sides. They can transmit power on two faces simultaneously, ideal for serpentine drives, multi-shaft drives, or reverse drives in compact spaces. DA type has teeth aligned on both sides; DB type has teeth staggered by half a pitch.