VAX was a line of mainframe computers built by Digital Equipment Corp (DEC). From an engineering standpoint, DEC was pretty much hands-down the best, but their marketing efforts sucked, and although they did enjoy some success (on the technical superiority of both their machines and their operating system, called VMS) they were unable to sustain it. DEC eventually was bought out by Compaq in the late 90's, which itself was bought out by HP a few years ago.
An excellent Wiki article summary of DEC can be found here
As a side comment, VMS was a *real* operating system, and not even Linux offers some of the same features that just came standard. In addition to having 4 user levels (system, group, owner, world) and 4 file permission settings (read, write, execute, and delete) VMS included automatic version control -- the first version of a file was called "file.txt;1" and each subsequent edit would increment the counter by one. The number of versions could be unlimited, or capped at a maximum, and what was so great about it was that if you needed to, say, retrieve a file as it existed 14 versions ago, you could. VMS likewise had 4 digit years built-in. The "Y2K" issue simply didn't apply to VMS itself (although obviously it could apply to poorly written applications that were running on VMS).
Just my 2 cents, but even though I only used VMS for a couple of years, it rocked. -- J.W.