Tallow is a rendered form of beef or mutton fat, primarily made up of triglycerides.

In industry, tallow is not strictly defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain technical criteria, including its melting point. Commercial tallow commonly contains fat derived from other animals, such as lard from pigs, or even from plant sources.

The adjacent diagram shows the chemical structure of a typical triglyceride molecule.

The solid material remaining after rendering is called cracklings, greaves, or graves. It has been used mostly for animal food, such as dog food.

In the soap industry and among soap-making hobbyists, the name tallowate is used informally to refer to soaps made from tallow. Sodium tallowate, for example, is obtained by reacting tallow with sodium hydroxide (lye, caustic soda) or sodium carbonate (washing soda). It consists chiefly of a variable mixture of sodium salts of fatty acids, such as oleic and palmitic.