BITNET /bit'net/ n., obs. [acronym: Because It's Time NETwork]
   Everybody's least favorite piece of the network (see {the network}) -
   until AOL happened. The BITNET hosts were a collection of IBM dinosaurs
   and VAXen (the latter with lobotomized comm hardware) that communicate
   using 80-character {{EBCDIC}} card images (see {eighty-column mind});
   thus, they tend to mangle the headers and text of third-party traffic
   from the rest of the ASCII/{RFC}-822 world with annoying regularity.
   BITNET was also notorious as the apparent home of {B1FF}. By 1995 it
   had, much to everyone's relief, been obsolesced and absorbed into the
   Internet. Unfortunately, around this time we also got AOL.


Source: The Jargon File

BITNET
     Because It's Time NETwork (network)
     
     
Source: Virtual Entity of Relevant Acronyms