The small ball-like structure on the right and left sides of the mouth and pharynx is called tonsil. There are three types of tonsils in the human body. Palatine, adenoid (pharyngeal) and lingual. It produces antibodies and lymphocytes to fight bacteria and viruses. Many times tonsils are infected by viruses and bacteria. It is called tonsillitis. Surgical removal of tonsils is called tonsillectomy.