What is a lipid bilayer?

Flexi Says:
The plasma membrane (also called the cell membrane) is a lipid bilayer that is common to all living cells. Its function is to keep the cell as a distinct entity in a water-based environment. A phospholipid bilayer is a double layer of closely-packed phospholipid molecules. It is this orientation of the phospholipids into the bilayer that biochemically gives the membrane its specific functional characteristics.