Anchovies are small, common saltwater forage fish in the family Engraulidae that are used as human food and fish bait. There are 144 species in 17 genera found in the Atlantic, Indian, and Pacific Oceans. Anchovies are usually classified as an oily fish. They are small, green fish with blue reflections due to a silver longitudinal stripe that runs from the base of the caudal fin. They range from 2 centimetres (0.79 in) to 40 centimetres (16 in) in adult length, and the body shape is variable, with slenderer fish in northern populations.
A traditional method of processing and preserving anchovies is to gut and salt them in brine, allow them to mature, and then pack them in oil or salt. This results in the characteristic strong flavor associated with anchovies, and their flesh turns deep grey. Anchovies pickled in vinegar, as with Spanish boquerones en vinagre, are milder, and the flesh retains a white color. For domestic use, anchovy fillets are sometimes packed in oil or salt in small tins or jars, sometimes rolled around capers. Anchovy paste is also available, as is anchovy essence. Anchovy mash is also sold in the UK under the label of Gentleman’s Relish as per the Two Fat Ladies cooking show.