What is the difference between a boil and carbuncle?

Single vs multiples: Boils and carbuncles are painful, pus-filled bumps that form under your skin when hair follicles become inflammed and infected by bacteria. Boils (furuncles) usually start as red, tender lumps. The lumps quickly fill with pus, grow larger and more painful until they rupture and drain. A carbuncle is a cluster of boils that form a connected area of infection under the skin.