From The School of Biomedical Sciences Wiki
Plasma proteins are proteins that are found within the blood stream. They are sometimes termed serum proteins.
The most common type of plasma protein is albumin which has roles in maintaining the osmotic pressure of the blood and transporting insoluble molecules such as lipids or hormones.
Other important types of plasma proteins are fibrinogens and globulins. Fibrinogens are important in blood clotting and globulins have important roles in the immune system.