A moratorium is the practice of suspending the sales of films on home video DVD, VHS, and Blu-ray and boxed sets after a certain period of time.
In 2002, Universal Pictures used this practice with the release of the Back to the Future DVD boxed set due to widescreen framing problems.
George Lucas also used this practice with the 2004 Star Wars original trilogy DVD boxed set.
A normal DVD that is sold under moratorium can sell at retail for a very high price relative to the general run of DVDs.
Additional unintended side-effects to the practice of moratorium had made films a prime target for internet piracy and bootleg sales.