What are "background data"?
One could talk about "foreground data" when referring to explicitly triggered downloads, or webpages retrieved interactively using a browser. Opposed to that, several services transfer data in the brackground, without the user explicitly triggering this. Examples include, but are not restricted, to...
- synchronizing your contacts and calendars with Google services
- updating location information, e.g. with Latitude
- Google Play (and other apps) checking for updates
Some apps, including the Google-Play app, require background-date to be enabled. Depending on device, Android version, and ROM, the corresponding setting might be found in different places:
- Settings→Accounts & Sync
- Menu→Settings→Battery data manager→Delivery
With Google Play and your contacts/calendar sync depending on background data being enabled, in most cases it's not a good idea to completely disable them -- even though some misbehaving apps might use it too much. A How-To shows what you can do instead to gain control (at least with Android 4.0 and higher).
- data-connection: for issues with your mobile data connection
- data-plan: a fixed amount of data included with your regular fee
- data-traffic: amount of data transferred. Use this for questions/issues like finding out which app is eating up your data plan.
- wi-fi: using your home WiFi network
- bluetooth: another wireless technology, but limited to short distances.
- usb: this can also be used to transfer data, but is not wireless.
- mobile-data: transferring data via your mobile data connection (2g/3g/4g)