Meaning of "forename" in British English?

I'm an American applying to do graduate study in the UK, and I'm stuck on the part where I put my name in (and really trying hard not to view this as a bad sign, lol). It's asking for "forenames" (plural) to go with my surname, but I've never heard the term "forename" before. Should I put both my first and middle name in as forenames, or just my first name? Thanks for any help!