Quick meaning
Recovering your phone's data, apps, and settings from a previously saved backup.
Think of it like this
Like using a spare key to reopen your home after losing the original.
Where you may see this
You may see this inside app stores, app settings, software updates, and install instructions.
Why it matters
Knowing the term helps you understand what an app is asking you to do before you tap, install, or change anything.
Say it simply
Restore from Backup means: Recovering your phone's data, apps, and settings from a previously saved backup.