British dairy topping for scones, toast, etc. It seems a bit like a cross between butter and cream cheese, but with a lighter texture and flavor than either. Clotted cream is made by heating whole unpasteurized milk, then removing the coagulated cream. Minimum 55% milkfat.

Sources:
http://www.foodtv.com/terms/tt-r2/0,1991,1362,00.html
http://www.culinary.com/gloss/glos-c.html
http://polaris.digistar.mb.ca/homepg/rbrandt/c.htm

Side note: for an interesting example of net.plagarism run a search on "Clotted cream can be refrigerated, tightly covered"