Due to concerns about political correctness at colleges and universities particularly in the United States, as well as a desire among academics to seem to know Latin, the preferred terms on college campuses now are generally "alumnus" and "alumna." It is regarded as politically incorrect, and arguably grammatically incorrect, to use "alumnus" and "alumni" to refer to women, but some people still stubbornly use those terms that way.
And, if one considers all-women colleges, they graduate only an "alumna", plural "alumnae," and on the grounds of ordinary correctness (non-political), they do only name their associations of graduates, alumnae associations.
One school, Texas A&M University, avoids the controversy completely. It has never called its graduates "alumni" or even "graduates", but "former students".