a real world point of view
CBS/Fox Video was a home video company formed and established in 1982 by the split-up of the former MGM/CBS Video (MGM went off to form MGM/UA Home Video).
The company was responsible for distributing VHS home videos of Doctor Who episodes to North American consumers from the 1980s until the summer of 2000, when distribution was handed off to Warner Home Video.
Initially, the tapes were marketed under CBS/Fox's "Playhouse Video" imprint, which was a label targeted towards children. The boxes for these releases carried the Playhouse label instead of the CBS/Fox one. Around 1990 (after "The Deadly Assassin" had been released), they started to use the normal CBS/Fox (and later, Fox Video) logos instead of Playhouse.
All of CBS/Fox's releases were identical in content to the original UK-PAL versions bar one: "The Deadly Assassin" was released in an edited (approx. 85 minute) movie version and was also notable for being the only time that a Doctor Who story was released in North America before anywhere else (until Warner Video released Series 1 of The Sarah Jane Adventures in North America before the UK). When the story was finally released in the UK, however, it was in its original episodic format. CBS/Fox also issued the controversial edited-down version of The Brain of Morbius, though a full-length version was issued later.