Disney Vault

The Disney Vault was a practice of artificial scarcity where several movies in the Disney Animated Canon were withdrawn from circulation on home video for several years.

Background
This had its origins before the advent of VHS, as Disney would re-release their movies in cinemas until the 1990s. This generated great publicity (the 1987 re-release of mh:greatestmovies: Snow White & the Seven Dwarfs was more hyped than many new releases at the time).

The practice extended to home video, where releases of the same movie would be ten years apart.

Movies that had been vaulted
Much of the Disney Animated Canon up to The Lion King had been vaulted.

As well as those films, Song of the South was also never released in the US on home video due to its outdated depiction of African-Americans. In fact, it's nearly lost to time, and most likely for the better too.

Disney+ and the end of the vault for Disney movies
When Disney's streaming service Disney+ (launched in the United States on November 12, 2019) was announced, Disney CEO Bob Iger revealed that the service will contain Disney's entire film library, which would de facto retire the concept of the Disney Vault as a home video control device (except for the aforementioned Song of the South). However, a separate practice restricting repertory screenings of films from the Disney back-catalogue remains in effect. Following Disney's purchase of 21st Century Fox for its entertainment assets (including 20th Century Fox) in March 2019, Disney withdrew the Fox film library from distribution to theaters, effectively placing the Fox back-catalog in the Vault. This caused an uproar from many cinema owners, as it meant they couldn't screen favorites like mh:greatestmovies:Die Hard around the holiday season. The only 20th Century Studios movie that wasn't vaulted was mh:greatestmovies:The Rocky Horror Picture Show due to its huge cult and LGBT following, and it was added on Star for Disney+.

Some Disney shows are currently not available on Disney+ for unknown reasons, either because Disney did not have the money to add them to their platform, or they were forgotten about long since they ended their run. Examples include House of Mouse, JoJo's Circus, Stanley, PB&J Otter, Mh:terribletvshows:The Shnookums and Meat Funny Cartoon Show, Mh:besttvshows:Bear in the Big Blue House, Bunk'd, and Aladdin: The Series.

They have also vaulted 4K Blu-ray releases of older 20th Century Studios films as well, provoking uproar from collectors.