Timing belts are found on most cars that were built in the 1990s or earlier. Some manufacturers have been switching to timing chains that are supposed to last the life of the engine. You can look in your owner’s manual to see what is in your car and when they recommend changing the belt if you have one. Generally, it’s at 60,000 miles or five years, whichever the happens first.
The timing belt sits along one side of the engine and keeps the crank and camshafts timed correctly. Its job is to make sure that these two components of the engine are synced. If it snaps, the type of timing configuration in your car (interference or non-interference) will determine what happens next. Jalopnik has a great explainer that breaks down these more technical aspects.
In an interference engine, the valve’s stroke and piston’s stroke happen in the same space in the cylinder and the timing belt makes sure they don’t hit each other. A snapped belt likely means damage that could range from bent valves to cylinder wall damage. The piston and valves are in different spaces on non-interference engines, so you all you need is a new belt and you’re off. Your best bet is to make sure you follow that scheduled maintenance so you don’t end up stuck on the side of the road with a broken belt and a potentially costly repair.