normally the gamma globulins which make up antibodies are a mixture of a huge number of different types. When nearly all gamma globulin being produced is one particular form this is called monoclonal gammopathy.

a disturbance in the synthesis of immunoglobulins; proteins having antibody activity increase greatly in the blood

An excess of gamma globulin (which includes antibodies, or immunoglobulins) in the blood. In the condition called monoclonal gammopathy of unknown significance, or MGUS, an abnormal amount of a single immunoglobulin is present in the blood, but there are no other signs or symptoms of cancer. Patients with this condition may develop multiple myeloma, other plasma cell tumors or lymphoma.