BITNET came to mean "Because It's Time Network", although the original meaning was "Because It's There Network".
It was composed only of educational institutions, although its protocols were used for a huge IBM internal network, which was larger than other networks such as ARPAnet for quite a while. BITNET links originally ran at 9600 baud. The BITNET protocols were eventually ported to non IBM mainframe operating systems.
At its zenith (circa 1991), BITNET extended to almost 500 organizations and 3,000 nodes.
With the advent of TCP/IP systems and the Internet in the early 1990s, BITNET's popularity and use diminished quickly.
BITNET featured e-mail and the Listserv software, but predated the World Wide Web, FTP and Gopher. You could also send short messages to other users (a feature exploited by BITNET Relay Chat), as well as files. BITNET's first electronic magazine, VM/COM, began as a University of Maine newsletter and surfaced broadly in early 1984. Nine years later, a University of Maine student would also publish the first WWW magazine.
One joke about BITNET was that it stood for "Because Idiots Type Network".