Pain de campagne is a big round loaf with a chewy, thick crust. It can be made with white flour, rye flour and / or “farine bise” (aka Farine de Blé Type 80.) These last two flours are mixed in with the white, which remains the predominant flour.
It is made from a starter, and contains no fat: just starter, flour, water and salt.
The bread usually has slashes on the loaves. This practice dates back to the communal ovens, which were owned by the seigneur or the state, who supplied the ovens (and who frowned upon people having their own, as they collected taxes from the use of the ovens.) You identified your loaves from your style of slashes.
The slashes served another purpose as well, in that they stopped bubbles from forming at the top of the dough which when cooked would expand and burst the top of the loaf open.