Olive oil is a liquid fat obtained by pressing whole olives, the fruit of Olea europaea, a traditional tree crop of the Mediterranean Basin, and extracting the oil.

Olive oil contains small amounts of free fatty acids. Free acidity is an important parameter that defines the quality of olive oil. It is usually expressed as a percentage of oleic acid in the oil. As defined by the European Commission regulation No. 2568/91 and subsequent amendments, the highest quality olive oil must feature a free acidity lower than 0.8%. Virgin olive oil is characterized by acidity between 0.8% and 2%, while lampante olive oil features a free acidity higher than 2%. The increase of free acidity in olive oil is due to free fatty acids that are released from triglycerides.