A Device performs one or more functions.
In the cyber world, the Internet domain, a Device is a personal tool for interacting with others on the Internet.
In order to be useful a Device must have one or more Apps (Applications) on it.
Thr most ubiquitous App is the Internet Browser.
There being multiple Browser developers standards have been developed by which HTML ( Browser language) is uniformly implemented.
Also, the Browser developers have developed controls which limit HTML developers` ability to gain control of your Device.
Not so with App developers. Their programs are self contained and have no controls on their programmed functions other than by the developer.