Quick meaning
An app that comes pre-installed on your device by the manufacturer and is essential to how it runs.
Think of it like this
Like the fittings in a new flat — they were there when you moved in and the flat needs them to function.
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
System App means: An app that comes pre-installed on your device by the manufacturer and is essential to how it runs.