In the most basic of terms, a belt (in the power transmission sense) is a flexible component that links two or more shafts together and transmits power and motion from one shaft to the other(s).
Belts can transmit power across a distance between shafts. Belt drives can increase or decrease the speed at a driven shaft or set of shafts. Belt drives can multiply the torque available at the driven shaft.
There are two broad categories for belts: Synchronous belts and V-belts.
Synchronous belts have teeth on the belt - you are most likely familiar with the timing belt on your car - which is a synchronous belt.
V-belts have a V shape (duh), and wedge into V shaped grooves in the pulleys (which are called "sheaves" in the industry).
That's all for this post....we'll grow and develop content as subject matter and reader interest dictates.