At one time, depending on who you asked, the letters "DVD" stood for either Digital Video Disc or Digital Versatile Disc. There is a lot of conflicting information out there on the web - the more plausible sources seem to indicate that the "V" originally for "Video", way back when the standard was being discussed and designed, but, in recognition of the fact that the discs could be used for more than just movies, was changed to "Versatile" before things were finalised.
Then, because it sounds less clunky, some people tended to refer to them as "Digital Video Discs" anyway, leading to some confusion over what they officially stand for (because we geeks worry about that kind of thing.)
In exasperation, the industry now appears to be settling on the "official" line that the letters don't stand for anything in particular, rather like MMX and the "NT" in Windows NT.