Eggs in Staub Mini Cocottes. Andreas Hartmann / flickr / 2015 / CC BY-SA 2.0
A cocotte is an ovenproof dish. It can be made of ceramic or cast iron (enamelled or plain.)
It is usually thought of as ramekin size, for baking eggs in, as in “oeuf cocotte” which is shirred eggs. This size often has no lid. But they can be large, 5-quart ones with lids, used on top the stove for braising and simmering, and popped in the oven for baking.
These larger ones, essentially what one would call casserole dishes in English, are sometimes referred to as “French ovens.” They can be used with any heat source (save microwave, for the metal ones.)
Some larger ones have lids that have short spikes protruding on the underside, to concentrate where the dripping happens so that the food cooking inside becomes self-basting.
French cocotte, non-enamelled, AV brand, circa 1930. Ptyx / wikimedia / 2019 / CC BY-SA 4.0