That's how the fair folk get you

While true, in that there is not formal rule, most do differentiate between fairy and faerie, and fairy and fae, and everything and the fair folk. Usually it depends on whether or not they want powerful dangerous non-human beings or dainty little beings with wings, etc.... You'll also see Sidhe (pronounced "she") when referencing almost all of the above too. I have seen some books use fairy, faerie, fae, and fair folk all used in the same story. Just makes it more fun to read.