Lubricants are substances typically used to reduce friction between parts in contact but, depending on the type, they also perform various other functions such as heat regulation, power transmission, sealing against dust or dirt, as well as reducing oxidation and preventing corrosion. They come typically in liquid form (water, natural or synthetic oils), semi-solid form (greases), solid form (pastes) but also in other forms. Depending upon the application, one type of lubricant will work better then another.

Different Piston and Turbine Engine oils (abbreviated as PEO and TEO respectively) form a type of lubricants used in general aviation, commercial and military aircraft engines, automotive, marine engines and other industrial applications,