Ready-made, self-updating content: dashboards, calendars, news, and the rest.
An app is content that keeps itself current. You configure it once and it looks after itself, pulling live data every time it plays.
Apps come with your subscription. There is nothing extra to buy, nothing to host, and nothing to install on the device.
What an app is, how it differs from other content, and where the code actually runs.
Installing one from the store, filling in its settings, and connecting it to a service that needs a login.
Running the same app several times with different settings, keeping apps on brand, and removing one.
Asking for an app, and building one yourself.