Lubricants are substances introduced between moving surfaces in relative motion to reduce friction, wear, and generation of heat. They act as a protective film that prevents direct metal-to-metal contact and improves efficiency of machines. The mechanism of lubrication can be understood primarily in terms of film formation. When a lubricant is applied, it forms a thin layer that separates the solid surfaces, thereby reducing interfacial adhesion and shear resistance. Depending on operating conditions, lubrication may occur through different mechanisms such as hydrodynamic, boundary, and extreme pressure lubrication. In hydrodynamic lubrication, a thick film of fluid completely separates the two surfaces, minimizing direct contact. Boundary lubrication occurs when the lubricant film is very thin and surface asperities may come in partial contact, where additives play a significant role. Extreme pressure lubrication happens under very high loads or temperatures, where special chemical additives react with the surface to form protective layers.