Background processing means something happening in the background and not literally visible to user.
Any task that takes more than a few milliseconds should be delegated to a background thread.
To keep our app responsive all time is an important part while developing an Android application, .

Making a network request on the main thread causes the thread to wait, or block, until it receives a response.
Since the thread is blocked, the OS can’t call onDraw(), and our app freezes.
It can lead into an Application Not Responding (ANR) dialog

An app is considered to be in the foreground if -
1. The app has a visible activity/fragment
2. The app has a foreground service
3. Another foreground app is connected to the app, either by binding to one of its services, or using one of its content providers
For ex. IME, Wallpaper service, Voice…