I don't think any grammarian would call it a relative pronoun as it doesn't begin a relative clause. In Scandinavian grammar it is simply an interrogative pronoun, which in this particular example begins an indirect question, though. Anglo-Saxon grammarians probably call it something else because it is followed by a noun.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
yellowstarstruck. Do you know what food this is?'What' is an interrogative adjective modifying 'food'.