An abscess is a tender mass of puss that generally forms around the teeth, armpits, base of the spine and in your groin.
The vast majority are caused by infection of a hair follicle and the skin within proximity of it, however antibiotics will not cure an abscess on its own.
Generally, they must be drained and opened in order for it to heal completely. Sometimes this happens on its own, however, in some cases a doctor must drain the boil of fluid in order for it to heal correctly.