Qualifies music for which the
sound material was manipulated or created by
electronic means.
As you see, the definition can embrace quite a large breadth of musical sub-genres. And it can get even broader if you use a definition stating that any music that use electronics as a means of reproduction is electroacoustic (some theoreticians use the term in such a way). However, the term is most often used to describe music that descends directly from classical electronic music and musique concrète. As a matter of fact, the term appeared when those two musical aesthetics cross-bred.
Some of the earliest examples of electroacoustic music include Edgar Varèse's Déserts (1954) and Karlheinz Stockhausen's Gesang der Jünglinge (1956).
Some of the best examples of electroacoustic music in this noder's opinion include Bernard Parmegiani's De Natura Sonorum and Pierre Henry's Apocalypse de Jean. Among many others.