Alumni & Friends

what do they mean by alumni here?

Plural of “alumnus”:

So it means former students and former friends??

Does it always use in school system or elsewhere?

The definition I linked to says it all I think. “alumni” usually refers to ex-attendees of an educational institution of some sort. It can sometimes also refer to ex-members of other types of institution or organisation.

“Alumni and Friends” doesn’t mean “former students and former friends”, it means former fellow students (probably) and other people who aren’t alumni but are considered (current) friends.