A lymphocyte is a type of white blood cell integral to the immune system, responsible for defending the body against pathogens. There are two primary types: B lymphocytes, which produce antibodies to neutralize foreign invaders, and T lymphocytes, which can directly kill infected cells or help coordinate the immune response. Lymphocytes originate from stem cells in the bone marrow but migrate to the lymphoid organs, such as the thymus and lymph nodes, for maturation and activation. Their vital role in recognizing and responding to specific antigens is essential for maintaining immune health and preventing diseases.