Anti-CD20 monoclonal antibodies (mAbs) are a type of drug used to target and deplete B cells, which are immune cells that play a role in various conditions. They are primarily used in the treatment of B-cell malignancies like non-Hodgkin's lymphoma and chronic lymphocytic leukemia, but also in autoimmune diseases. Rituximab is a well-known example of an anti-CD20 mAb.