Difference between a timing belt and a V-belt?

A V-belt, in cross section, is shaped like a triangle with the bottom cut off. It is intended for use on a V shaped pulley. These were frequently used to drive automotive accessories (power steering, air-conditioning, alternator) in the days before the serpentine belt system became in vogue. The middle 1970s would be my guess as to when most manufacturers switched to the serpentine belt system. The classic v-belt is the most tried and true style of v-belt in the market. Originally designed to replace leather belts in a variety of industries including agriculture, facility maintenance, heating ventilation and air conditioning (HVAC), rock crushers, oilfield supply and material handling.

A timing belt us usually made with a cogged belt and cogged pulleys- because in a timing belt any slippage is bad. A cogged belt is flat on the outside and on the inside there is a series of either square or rounded strips running perpendicular to the belt that coincide with cogs on the driven pulleys.
www.rubberbeltmanufacturer.com