The outer covering of an animal cell is called the plasma membrane or cell membrane. It is a thin, flexible, and semipermeable barrier that surrounds the cell and protects its contents. The cell membrane is composed of a phospholipid bilayer, which is a double layer of phospholipids, along with embedded proteins and carbohydrates. The phospholipids form a barrier that prevents water-soluble molecules from entering or leaving the cell, while the proteins and carbohydrates provide various functions such as cell adhesion, transport, and signaling.