DRM Digital Rights Management
Technology that restricts what you may do with content you have paid for.
The underlying problem is unsolvable: to display the film the device must decrypt it, so the key is in the user's hands. All DRM is therefore delay rather than protection — you raise the cost of copying and rely on law for the rest.
On the web it is implemented through EME with modules such as Widevine (Google), FairPlay (Apple) and PlayReady (Microsoft), often combined with HDCP over HDMI. Widevine's security levels are what actually decide whether you get 4K or settle for 480p in Firefox on Linux.