Leviticus 7:23 - Ellicott's Commentary On The Whole Bible

Ye shall eat no manner of fat. — That is, the fat of beeves, sheep, or goats. The fat of these three kinds of sacrificial quadrupeds is prohibited, even when they are not killed as sacrifices, but when slaughtered for private consumption; but the fat of other tame or wild clean quadrupeds, as stags, roes, &c. &c, was lawful. According to the practice which obtained during the second Temple, there are three kinds of fat for the eating of which a man incurred the penalty of excision: the fat (1) which is upon the inwards, (2) upon the two kidneys, and (3) upon the flanks (Leviticus 9:10). The rump, the kidney, and the caul above the liver were not called fat, except in sacrifices. The fat which is covered with flesh is lawful, the fat upon the kidneys is forbidden; but that which is within the kidneys, as well as that of the heart, is lawful.