The lubrication system has three purposes, or uses. First, it reduces the friction between parts that move. Secondly, it takes heat away from the engine. And lastly, it cleans engine parts as it lubricates them.
Friction is severe along the surface of the piston where it touches, or rubs, against the cylinder wall. Pistons and cylinders must be well lubricated in order to prevent overheating and reduce wear. There are many other parts of the engine that must also have lubrication in order to reduce wear and tear.
An oil pump, an oil gauge (gage), and an oil filter, or cleaner, are parts of the lubrication system. The oil pump circulates, or moves, the oil to the various engine parts that need lubrication. An oil gauge is used for the purpose of showing the pressure of the oil. An oil filter cleans, or filters, the oil.