Olive oil is a fat obtained from the olive (the fruit of Olea europaea; family Oleaceae), a traditional tree crop of the Mediterranean Basin. The oil is produced by grinding whole olives and extracting the oil by mechanical or chemical means. It is commonly used in cooking, cosmetics, pharmaceuticals, and soaps and as a fuel for traditional oil lamps. Olive oil is used throughout the world, but especially in the Mediterranean countries.

The olive tree is native to the Mediterranean basin; wild olives were collected by Neolithic peoples as early as the 8th millennium BC. The wild olive tree originated in Asia Minor in modern Greece.

It is not clear when and where olive trees were first domesticated: in Asia Minor in the 6th millennium; along the Levantine coast stretching from the Sinai Peninsula to modern Turkey in the 4th millennium; or somewhere in the Mesopotamian Fertile Crescent in the 3rd millennium.

A widespread view exists that the first cultivation took place on the island of Crete. Archeological evidence suggest that olives were being grown in Crete as long ago as 2,500 B.C. The earliest surviving olive oil amphorae date to 3500 BC (Early Minoan times), though the production of olive is assumed to have started before 4000 BC. An alternative view retains that olives were turned into oil by 4500 BC by Canaanites in present-day Israel.

The olive ( /ˈɑːləv/ or /ˈɒlɨv/, Olea europaea, meaning "Oil from/of Europe") is a species of small tree in the family Oleaceae, native to the coastal areas of the eastern Mediterranean Basin (the adjoining coastal areas of southeastern Europe, western Asia and northern Africa) as well as northern Iraq, and northern Iran at the south end of the Caspian Sea.

Its fruit, also called the olive, is of major agricultural importance in the Mediterranean region as the source of olive oil. The tree and its fruit give its name to the plant family, which also includes species such as lilacs, jasmine, Forsythia and the true ash trees (Fraxinus). The word derives from Latin olīva which in turn comes from the Greek ἐλαία (elaía) ultimately from Mycenaean Greek 𐀁𐀨𐀷 e-ra-wa ("elaiva"), attested in Linear B syllabic script. The word 'oil' in multiple languages ultimately derives from the name of this tree and its fruit.

The olive tree, Olea europaea, is an evergreen tree or shrub native to the Mediterranean, Asia and Africa. It is short and squat, and rarely exceeds 8–15 metres (26–49 ft) in height. The silvery green leaves are oblong, measuring 4–10 centimetres (1.6–3.9 in) long and 1–3 centimetres (0.39–1.2 in) wide. The trunk is typically gnarled and twisted.

An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils.

First attested in English 1176, the word oil comes from Old French "oile", from Latin "oleum", which in turn comes from the Greek "ἔλαιον" (elaion), "olive oil, oil" and that from "ἐλαία" (elaia), "olive tree". The earliest attested form of the word is the Mycenaean Greek e-ra-wo, written in Linear B syllabic script.

Organic oils are produced in remarkable diversity by plants, animals, and other organisms through natural metabolic processes. Lipid is the scientific term for the fatty acids, steroids and similar chemicals often found in the oils produced by living things, while oil refers to an overall mixture of chemicals. Organic oils may also contain chemicals other than lipids, including proteins, waxes and alkaloids.

Lipids can be classified by the way that they are made by an organism, their chemical structure and their limited solubility in water compared to oils. They have a high carbon and hydrogen content and are considerably lacking in oxygen compared to other organic compounds and minerals; they tend to be relatively nonpolar molecules, but may include both polar and nonpolar regions as in the case of phospholipids and steroids.

Michael A. Klaper, M.D., is an American physician, author, and vegan.

Dr. Michael Klaper spent much of his childhood vacations on his uncle's dairy farm in Wisconsin.

Dr. Klaper graduated from the University of Illinois College of Medicine in 1972 and served his medical internship at Vancouver General Hospital with the University of British Columbia. He also studied obstetrics at the University of California in San Francisco.

After graduation, Klaper moved between a number of locations, practiced acute care medicine, and eventually became certified in urgent care medicine. Following a desire to lead a less violent life, Klaper became a vegan in the early 1980s.

He served as director of a vegan health spa in Pompano Beach, Florida from the early 1990s, where he observed the healing powers of plant-based nutrition, and was featured on the PBS documentary Diet For A New America by John Robbins. However financial realities required him to return to urgent care medicine, which led him to practice in Maui, Hawaii, between 1995 and 2006, and Whangarei, New Zealand, between 2006 and 2009. In 2010, he returned to nutritional medicine and currently serves on the medical staff at the TrueNorth Health Center in Santa Rosa, California.