A carbuncle is a cluster of boils caused by Staphylococcus aureus infection of the subcutaneous tissue, commonly occurring in diabetic patients or those with poor immunity. It presents as a red, swollen, and painful lump, usually on the neck, back or shoulders. Risk factors include diabetes, poor hygiene, weak immune system, and activities that break the skin. Treatment involves antibiotics, pain relief, improving health, and potentially surgery to drain pus if multiple abscesses form.