An offset smoker is a smoker whose firebox is attached to the side of the cooking chamber.
In this design, a separate fire burns in a smaller chamber, while heat and smoke travel through an opening or connecting pipe into the larger food chamber. The meat cooks indirectly, with airflow controlled through vents and the smoke eventually leaving through an exhaust chimney.
Offset smokers are commonly cylindrical and are strongly associated with traditional American barbecue. They may burn wood, charcoal, or both. A reverse-flow offset is a related variation: a baffle plate directs heat beneath the food before it rises, helping reduce hot spots and even out temperatures.
The main mix-up is confusing an offset smoker with a vertical smoker or pellet smoker. “Offset” describes the physical arrangement of the firebox and cooking chamber, not the fuel. Pellet smokers, by contrast, use an auger-fed supply of compressed wood pellets.