Quick meaning
An alert telling you a new version of an app or system is available.
Think of it like this
Like a letter in the post saying a new edition of something you use is now available.
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
Update Notification means: An alert telling you a new version of an app or system is available.