There are, in fact, three
types of tonsils in the lymphatic system
of the human body
It is the palatine
tonsils to which people most commonly refer when they talk about their tonsils.
Tonsils are part of the bodies defense mechanism against disease. White blood cells pass through the tonsils and detect possible sources of infection, such as bacteria, which have entered the human body through the mouth or nose. Once detected by this early warning system, antibodies are created to subdue the foreign organism.
Since tonsils are in the front line when it comes to being exposed to infection, they can become infected themselves. This manifests itself as inflammation of the tonsils, (tonsillitis). Tonsillitis occurs most often in young children, since the tonsil tissue tends to retract as adulthood approaches, (presumably because other parts of the immune system are more developed by this time and the tonsils aren't so important in the defense against infection).