An oil filter is a device that removes contaminants from engine oil. It's a crucial component of an internal combustion engine, as it helps to maintain the cleanliness of the engine oil.

The primary function of an oil filter is to trap impurities, such as metal particles, dirt, and combustion byproducts, that can circulate in the engine oil. By doing so, it prevents these contaminants from damaging engine components, such as bearings, pistons, and cylinder walls.