I've heard different things. what exactly is carbuncle?

Bacterial infection: It is a boil on the skin which affects the deep portions of the area. It needs to be drained to allow the pus out. It will be packed and drainage will continue for a few days resulting in a scar at the site. If there are more than one lesion than oral antibiotics will be prescribed.

Carbuncle: A carbuncle is similar to a furuncle (boil) except that it has multiple openings and is usually larger. There can be a great deal of swelling and pain, so opening a carbuncle to get pus out and relieve pressure can help a lot with pain. Warm compresses and pain meds, especially anti-inflammatory meds, can help. I usually put the person on an antibiotic also.

A type of abscess : A carbuncle is a variant if an abscess where the infection and puss expands under the skin, causing swelling, pain, possibly fever, resulting in multiple draining areas of puss overlying the swelling mass of the infection. This is often treated by opening, draining the wound and packing it with gauze and antibiotics. If not treated properly it can cause a blood infection which is quite serious.