Some Albanian researchers claim that the name "Kosovo" is a Serbian form of an old Albanian placename meaning "high plain". However, this is not a widely accepted theory: it is generally believed that the name derives from the Slavic word kos (or "blackbird"). It is a widely used placename in Slav countries, used for a number of localities in Belarus, Bosnia, Bulgaria, Croatia and Russia. The Albanian form "Kosova" would thus be an Albanian version of a Slavic placename.