Tonsils are small masses of lymphoid tissue located at the back of the throat. They play a role in the immune system by helping to fight infections, particularly in children. The main types are palatine tonsils (the ones commonly removed during a tonsillectomy), adenoid (pharyngeal tonsil), and lingual tonsils. While they serve a protective function, they can also become inflamed or infected, leading to conditions such as tonsillitis.