Definition:
Alumni associations are organizations reuniting former students of a college or university and can be found at renowned educational institutions around the world.
Meaning:
The term alumnus (m; Pl.:-i) respectively alumna (f.; Pl.:-ae) has its origin in the Latin language. It means "pupil", literally "the nurtured" (origin: alere: nurture).
Students of a so called "alumnat" (boarding school) were called alumni/-ae.
Today the term alumnae/alumni usually refer to graduates of a university or a similar educational institution but it can also be used depending on the context and the individual point of view.
It may refer to a group of graduates of a university or, in broader sense, to all students and graduates of a university.
Tradition:
Since decades societies of former students (alumni societies) have been existing at universities in the United States and some European countries. For example, there is a long tradition of alumni societies in Great Britain and France. In Germany alumni societies were established in the late 1980s.
These societies give alumae/alumni the possibility to keep in touch with "their" university and former fellow students as well as to take advantage of advanced scientific training.