"Exogenous protein" refers to a protein that comes from outside sources, such as food or supplements, rather than being made by our own bodies. It is a term commonly used in the context of nutrition and biology.
Full definition
The immune system reacts to
exogenous proteins of bacteria and viruses, so - called antigens, by producing antibodies.
This agrees with a recent study that used a measure of biological value (BV, higher the better) to assess how
efficiently exogenous protein gets used for protein synthesis in the body.