How does OTA upgrade work?

I was trying to understand what exactly does it mean by OTA update?
I have come across some documents where it says the steps to do OTA upgrade and the nvidia related packages which are getting upgraded(NVIDIA Jetson Linux Developer Guide : Over-The-Air Updates | NVIDIA Docs). But as I understand it looks similar to the upgrade what we do in a normal linux system.
Rather than package upgradation, what does OTA upgrade do (in l4t 4.5) ?
Ashik P.

Some time ago all of the NVIDIA files used were just that…loose files, and not available as a package. This meant that any regular packages from Ubuntu had to be skipped if they would have overwritten this content. Then NVIDIA built their own package-based repository server. When that server is available it means updates can occur with apt even for the NVIDIA packages (which are now actual “.deb” packages and not loose files). So “Over the Air” (“OTA”) is basically setting up Jetson updates to more or less be mostly using the “standard” apt-get mechanism.

Thanks for the information @linuxdev .

It seems since then Nvidia added a bunch of components to the OTA