Timming belt what is a timing belt and where is it located?

It is a belt (similar to a serpentine belt which drives the alternator, power steering, water pump, etc.) which drives the camshaft from the crankshaft. The belt has cogs so it can't slip, and must be installed exactly right -- the crankshaft and camshaft must be correctly "timed" to work with each other. On many engines, if they are not correctly timed, or if the belt breaks, the pistons slam into the valves and the engine is essentially destroyed.
It is located under covers at the same end of the engine as the accessory drive belts, and requires a lot of tools, knowledge, and experience to replace correctly.