A clay oven (cob / earth / horno / adobe) is a hollow, dome-shaped structure constructed out of clay, clay and sand or clay and straw, used for the purpose of baking and roasting food. It has a brick floor and usually a chimney. Most traditional clay ovens are built outdoors. Cooking in a traditional clay oven is wonderful, it feels different and definitely tastes different.
You can save a lot of space in a clay oven as you can use the same space for fire to heat the oven up and then for cooking after removing the fire. The heat in a clay oven is also evenly spread and does not leave cold spots. Clay ovens stay hot for a long time too so you get ample time to cook your pizza.