A kiln is a special kind of oven for firing things like pottery and bricks. A ceramic artist might use a kiln once a week to fire the bowls he's made from clay.
Some kilns look more like furnaces than ovens, and they reach temperatures far beyond regular household ovens. Electricity is used to power many modern kilns, while others use older techniques of burning wood or even coal. Making mugs and bowls is the primary use of kilns, but there are some that dry lumber, tobacco leaves, or hops as well. The Old English word was cyln, from the Latin root culina, "kitchen or cooking stove."