Lubricant is a substance which is used to control (more often to reduce) friction and wear of the surfaces in a contact of the bodies in relative motion. Depending on its nature, lubricants are also used to eliminate heat and wear debris, supply additives into the contact, transmit power, protect, seal.
A Lubricant can be in liquid (oil, water, etc.), solid (graphite, graphene, molybdenum disulfide), gaseous (air) or even semisolid (grease) forms. The liquid lubricants can be classified based on the base oil to synthetic/semi-synthetic, mineral or environmentally acceptable (biodegradable) oils. Most of the lubricants contain additives (5-30%) to improve their performance.