An abcess describes a collection of pus and other infected tissue that occupy a discrete location in the body, but does not have an outer membrane (which is referred to as a cyst). They generally occur in parts of the body which have poor blood circulation as otherwise the blood carries these materials to the liver to be properly disposed of.
Although minor abscesses are not life threatening, larger ones can result in the infection entering the bloodstream, causing sepsis.
The standard treatment for an abcess is to lance it and let the pus drain out. However, this is not an option where the abcess is inaccessible or deep within the body. As such, large doses of broad spectrum antibiotics are the required treatment.