Quick meaning
The app that controls the appearance and organisation of your Android home screen.
Think of it like this
Like the interior designer of your phone's front page.
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
Launcher (Android) means: The app that controls the appearance and organisation of your Android home screen.