An alumna is a woman who used to study at a particular school, college, or university. It is the feminine of alumnus, kept from Latin, so it feels formal and a little ceremonial — the kind of word a university uses on invitations, in official histories, or when it wants to sound proud and traditional. In everyday American speech, many people just say alum and skip the gender marking. The plural of alumna is alumnae (often said like “alumn-ee” or “alumn-eye”); people mix that up with alumni, which is the masculine or mixed plural. Chinese 校友 does not force this male/female split, so English is being fussier here than Taiwanese usually needs to be.