Apps that run in the background can receive info, send notifications, and stay updated, even when you aren't using them -- which can be useful, but can also suck your battery and your data, if you're connecting via a mobile hotspot.
To control which apps are running in the background and save some battery power and data, go to Settings > Privacy > Background apps. To stop all apps from running in the background, toggle Let apps run in the background to Off. Or, you can choose which apps to run in the background individually by going down the list on the same page.
