Tonsils are small masses of lymphoid tissue located at the back of the throat, and they play a role in the immune system by helping to fight infections. There are three types of tonsils: palatine tonsils (the ones most commonly referred to), pharyngeal tonsils (adenoids), and lingual tonsils. They can become inflamed or infected, a condition known as tonsillitis, which may require medical treatment or even surgical removal in severe cases. Generally, tonsils help protect the body from pathogens entering through the mouth and nose.