B cell: A type of white blood cell, specifically a variety of lymphocyte. Some B cells develop into plasma cells, which are responsible for producing antibodies—proteins crucial for combating infections. Other B cells evolve into memory B cells. All plasma cells originating from a single B cell create identical antibodies that target the specific antigen that triggered their development. This concept also applies to memory B cells, meaning both plasma and memory cells "recall" the antigen that prompted their creation. In birds, B cells mature within an organ known as the bursa of Fabricius, while in mammals, they primarily mature in the bone marrow. Therefore, the B cell, or B lymphocyte, plays a significant role in the immune system. It does not rely on thymus-derived factors, has a relatively short lifespan, and is crucial for producing immunoglobulins, which are displayed on its surface.