Lipid

A lipid is a type of organic molecule found in living things. It is oily or waxy. Fats are made from lipid molecules. Sources of lipid can be found in algae, seeds, meat, cheese, butter and fish. Lipids are long chains of carbon and hydrogen molecules. Lipids are classified as simple and complex. Examples of complex molecules could be steroids or phospholipids. 
A very important biological function of lipids is as lipid bilayers, the basis of many cell membranes. Another function of lipids is to serve as an energy reserve. Lipids can be hydrophobic (non-polar), or amphipatic (containing both polar and non-polar parts).
Lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), glycerides, phospholipids, and others. The main biological functions of lipids include storing energy, signalling, and acting as components of cell membranes.