Quick meaning
An app made by a company other than the maker of your phone or operating system.
Think of it like this
Like a non-brand item in a supermarket — not made by the supermarket but sold there.
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
Third-Party App means: An app made by a company other than the maker of your phone or operating system.