Lubricants such as oils, greases, and other substances are used to reduce friction between moving parts and prevent wear. There are various types of lubricants including mineral, synthetic, vegetable, and animal-based. Oils are used for lubrication through boundary, hydrodynamic, and elastohydrodynamic methods. Greases are also used for lubrication and provide advantages over oils by remaining in contact with moving surfaces longer. Synthetic lubricants were developed to withstand higher operating temperatures than petroleum-based lubricants. Proper lubricant selection and maintenance is important for optimal machinery performance and longevity.