At Virginia Tech, I believe this was an acronym for Campus Branch eXchange.

Some time in the late 1980's or very early 1990's, VT installed a telephone network that included, revolutionary for its time, digital data connectivity. Instead of buying what at the time was a fairly expensive and somewhat rare device called a modem, students with their own computers (who weren't all that common themselves) could run a serial cable from their computer to a port on the back of the phone. This connected them to a text-based network, running at 19200 bps, from which they could reach such things as the library, Dropadd and other fun university computer systems without trudging through a foot of snow to a computer lab.

Fast forward to 1997. Most campus dorms now have Ethernet, but a few select hellholes are still on CBX. The CBX network has been hacked-to-hell to allow SLIP connections to the Internet, but hasn't been adequately maintained, so maximum transfer rate is now about 11600 bps. And, of course, there's only one of these connections per room containing two residents, when nearly every incoming freshman has a computer by now (which would be made mandatory the next year).

It's a wonder my freshman-year roommate and I didn't kill each other over this, despite getting along in most other facets. Assigning two computer science majors to one CBXed room was not a wise move. Fortunately, they finished wiring the entire campus by the next fall.

The amusing footnote to this story is that our freshman-year dorm, Barringer Hall, apparently had a reputation circa 1994 as a software piracy haven, along with a high return rate for upperclassmen (apparently, they liked it so much they didn't want to leave; I never quite figured out why). Urban legend had it that this rep was responsible for Barringer being dead last on the wiring schedule.