A lubricant is a substance introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces.

A good lubricant generally possesses the following characteristics:

• High boiling point and low freezing point
• High viscosity index
• Thermal stability
• Hydraulic stability
• De-emulsibility
• Corrosion prevention
• High resistance to oxidation.

Lubricants are used for three purposes-to reduce friction, to prevent wear, and as a protective cover against corrosion.