A carbuncle is a deep bacterial skin infection consisting of a cluster of interconnected boils (furuncles) involving adjacent hair follicles. It is usually caused by Staphylococcus aureus and forms a painful, pus-filled swelling that may drain through several openings, often on the back of the neck, shoulders, buttocks, or thighs. It can heal with scarring. Merck Manual definition

Carbuncle: a deep skin infection made up of a group of connected boils (furuncles) involving several adjacent hair follicles, usually caused by Staphylococcus aureus. It is painful, pus-filled, and may drain through multiple openings.

According to the classic description in Bailey & Love:

It commonly occurs at the nape of the neck and produces multiple discharging points with central slough.