A T cell is a type of white blood cell that plays a crucial role in the immune system. It helps the body fight off infections and diseases by recognizing and attacking pathogens, such as viruses and bacteria. T cells are produced in the bone marrow and mature in the thymus, which is where they get their name. There are different types of T cells, including helper T cells and cytotoxic T cells. Helper T cells assist other immune cells in responding to infections, while cytotoxic T cells directly kill infected or cancerous cells. Together, they help maintain the body's defense against various health threats.