The term "fat" may be applied to any of the following:

 

1. The glyceride ester of a fatty acid.

 

2. A lipid that is solid or semi-solid at normal body temperatures.

 

3. A mixture of lipids, chiefly triglycerides and associated phosphatides, sterols, alcohols, hydrocarbons, ketones, and related compounds, that is solid at normal body temperatures and occurs widely in organic tissue, especially in the subcutaneous connective tissue of animals and in the seeds, nuts, and fruits of plants.

 

Fats occur widely in plants and animals as a means of storing food energy, having twice the calorific value of carbohydrates. In mammals, fat is deposited in a layer beneath the skin (subcutaneous fat) and deep within the body as a specialized adipose tissue. The insulating properties of fat are also important, especially in animals lacking fur and those inhabiting cold climates.

 

In a saturated fat, the molecules contain only saturated fatty acids combined with glycerol. Fats derived from plants and fish generally have a greater proportion of unsaturated fatty acids than those from mammals. Their melting points thus tend to be lower, causing a softer consistency at room temperatures. Highly unsaturated fats are liquid at room temperature and are more properly called oils.