It's used in Moroccan cookery to make fabulously tasty sorta like a stew but still separate. It's two pieces: an earthenware plate with a rim, and a cone that fits tightly to that rim. The top of the cone has a small hole. One arranges the food on the plate, applies sauce, then into the oven to become delicious.

And the link tells me it's "tay GENE," so thanks for asking:
http://mideastfood.about.com/od/glossary/g/tagine.htm