Lymphocyte is a type of white blood cell that plays a crucial role in the body's immune system. They are responsible for recognizing and attacking foreign substances such as viruses and bacteria, as well as identifying and destroying abnormal cells such as cancer cells. Lymphocytes are able to specifically target and remember these foreign substances, allowing for a quicker and more effective immune response in the future. They are a specialized component of the body's defenses against infection and disease.