A more thorough explanation:

The Sony doctrine is a legal principle that refers to the routine use of a product in a way that does not infringe on intellectual property rights. It is also known as commercially significant noninfringing use. The principle is used to determine whether the sale of a product amounts to contributory infringement.

For example, if a product like a video recorder can be used in a way that does not infringe on intellectual property rights, such as recording a program to watch it later, then its sale cannot be stopped, and the manufacturer cannot be subjected to a court-imposed royalty.

The Sony doctrine was established in the case of Sony Corp. of America v. Universal City Studios, Inc. in 1984. The case involved the sale of Betamax video recorders, which were used to record television programs. The court ruled that the sale of the recorders was legal because they had substantial noninfringing use.

Another example of the Sony doctrine in action is the sale of MP3 players. While these devices can be used to infringe on copyright by downloading and sharing music illegally, they also have noninfringing uses, such as playing music that has been legally purchased or downloaded.

The Sony doctrine is important because it helps to balance the rights of intellectual property owners with the rights of consumers to use products in ways that do not infringe on those rights.