A tensioner is a mechanical device used to maintain tension in a system, such as a belt or chain. It ensures that the components remain tight and function properly, preventing slippage or wear. Tensioners are commonly found in automotive engines, where they help keep the timing belt or serpentine belt at the correct tension for optimal performance. There are different types of tensioners, including manual and automatic versions. Automatic tensioners adjust themselves based on the system's needs, while manual tensioners require periodic adjustments by the user. Proper tensioning is crucial for the longevity and efficiency of machinery, including engines and conveyor systems.