A phospholipid bilayer or lipid bilayer is a double layer of lipids in a cell membrane which has a hydrophobic and a hydrophilic part.
Hydrophobic - expelled by water
Hydrophilic - attracted to water
The layers form the cell membrane which means that it's functions are the same as the functions of a cell membrane, and are critic to the cells functioning.
Hope it helped,
BioTeacher101
