In very simple word, “A lubricant is a substance, usually organic, introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. The property of reducing friction is known as lubricity.”
Typically, lubricants contain 90% base oil (most often petroleum fractions, called mineral oils) and less than 10% additives & some solid lubricants (as per requirement 5 to 10%).
Mineral oils are produced from refined hydrocarbons obtained from crude oil by distillation. Mineral oil is any of various colorless, odorless, light mixtures of higher alkanes from a mineral source, particularly a distillate of petroleum, as distinct from usually edible vegetable oils.
Synthetic oils are manufactured polyalphaolefins, which are hydrocarbon-based polyglycols or ester oils. Although there are many types of lube oils to choose from, mineral oils are the most commonly used because the supply of crude oil has rendered them inexpensive.