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.