Fat is a low-value yellow animal product obtained by butchering an animal. It is found in globs, but unlike other globs will not be cleaned by dwarves. In its liquid form, it is named grease. Although it can ignite, fat cannot boil.
 Fortress Mode Use
 Adventure Mode Use
In Adventure Mode, fat is a portable solid, though it is hardly usable when in a solid state.
When fat is placed in a warmer temperature, (usually when placed in the fire that surrounds a burning tree/plant) it eventually becomes grease, which is then drinkable for a short while after before it cools back down into fat. You sometimes may notice a pool of grease being left behind from someone who was burning.
However, given the usual weight of fat, you might be better off using other liquids.
Most creatures have a layer of fat between skin and muscle, with notable exceptions of inorganic ones (such as iron men). Because of its relatively low melting point, the fat is usually the first thing to go if a creature burns.
Creatures may have varying levels of fat, even when of the same species or caste. In a dwarf's description, for example, it may state his relative amount of fat compared to the racial average. Fatter creatures give more fat when butchered than creatures that are less fat. The amount of fat on a creature is related to its size.