T Lymphocytes, also known as T cells, are a type of white blood cell that play a crucial role in the immune system. They originate from stem cells in the bone marrow and mature in the thymus gland. T cells are essential for identifying and attacking infected or cancerous cells in the body. There are several subtypes of T cells, including helper T cells and cytotoxic T cells. Helper T cells assist other immune cells in responding to pathogens, while cytotoxic T cells directly kill infected or abnormal cells. Together, they help maintain the body's defense against diseases.