User blog comment:7-45 Fire/YeahWinx (form) page has a flaw/@comment-31892545-20171125232113/@comment-29197449-20171126022333

Technically, Faragonda added the term "Winx" to the overall vocabulary to have it represent the modern fairy. Though, even with that, we can only assume that, as the best school for fairies in the Magic Dimension, Alfea would have some kind of authority over such things like naming an otherwise nameless base form.

Again, that's only an assumption though because it's never made clear that fairies from other schools (as much as they idolize the Winx) actually call their base forms "Winx." I feel like this would only be the case in the 4Kids dub because there, it's heavily implied that "Winx" is the essence of fairy magic. Then again, as much as people believe it to be set in stone, 4Kids isn't canon.