Typically it is a big pot. There are two kinds. A stove top one and a camp Dutch oven. The camp style has stubby legs so you can put coals under it, and a rim around the top so coals don't roll off. You can bake in it. I've made many cakes in them.

They're usually cast iron, but sometimes aluminum.

They come in different sizes. Most are between ten and twelve inches, or six and 8 quarts.