The fluid mosaic model is an interpretation of cell membrane structure. It was proposed in the early 1970s by S.J. Singer and Garth Nicolson. The fluid mosaic model says that cell membranes are composed of a double layer of lipids with associated proteins. The lipid bilayer, as it is commonly referred to, has a back to back structure - in the outer layer the hydrophilic heads of the lipid molecules are oriented outward, and in the inner layer they are oriented inward.
A variety of proteins are attached to and embedded in the lipid bilayer. The attached, or peripheral, proteins include identifiers, hormone receptors, and immune proteins. The embedded proteins create transport passageways for the many different molecules that need to be moved into and out of the cell. The "fluid" part of the term comes from the belief that the proteins are able to flow and move around in the membrane.
The YouTube link below has a nice animation that may help you to picture the fluid mosiac structure more clearly.
The fluid mosaic model was first proposed by S. J. Singer and Garth Nicolson in 1972. According to the model, biological cell membranes can be considered as a fluid mosaic model because the membrane components (lipids and proteins) are dynamic and ever-changing, and mosaic because the proteins are scattered about in this pattern. A mosaic is a structure made up of many different parts. Likewise, the cell membrane is composed of different kinds of macromolecules. The components of a plasma membrane are integral proteins, peripheral proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol and lipoproteins.
For more information on biological membranes, you can watch a relevant video here: http://www.youtube.com/watch?v=moPJkCbKjBs&feature=related