What exactly is lost/changed after a re-install of macOS?

I recently accidentally deleted some system files of macOS and thus, reinstalled macOS Big Sur in recovery mode. I have been assured that any data will not be lost, but I am wondering what exactly comes under ‘data’.

I assume it means files, apps etc. but what about things like my preferences for various apps and changes I made in system preferences? Or, my saved passwords in safari? Does that come under ‘data’?

Also, if possible, could you provide what exactly will be lost/ changed and what will not.

Note: Before my re-install, I was running the latest version of macOS I.e 11.4

All the things you list are user data and settings that the macOS upgrade and update and reinstalllation process will leave alone.

Time Machine has a compare feature where you could generate a delta between what is on disk and what the last backup interval saved.

• Find Differences between Time Machine backups

Basically, Data is what you did to change the stock Mac so files, pictures, apps you install and all the settings like time zone, Siri, sleep settings and more are all considered user data and not the system.