In the context of the PlayStation 4, a is essentially an installer package. It is the format Sony uses for digital downloads from the PlayStation Store, as well as for game updates and DLC. When you download a game legally, the console downloads these packages in the background and installs them automatically.

: If you have a subscription, you can claim "Monthly Games" at no extra cost and access a large "Game Catalog" depending on your tier. Demos and Betas