"installer or updater" predefined policy

Hi all,
strange enought I’m not able to find a place where it is explained what “installer or updater” predefined policy really means.
I’m able to understand what, for example, means “Windows system application” by looking at the access rights settings (and it means “all granted”) and what means “Trusted application” (that is “all granted except run an executable”), but what means “installer or updater” is a mistery to me, as it is not present on the predefined security policy control pane.
So, the question is:
What does really means “installer or updater” policy.
Why, inside “computer security policy” I found “explorer.exe” bound to “installer or updater” and not bound to another policy such as “Windows system application”?
What’s the difference?

Greetings.
Alessio