Two questions of "Delete" and "Unlink" in outliner

Support Basics & Interface
1

I’ve read these two manual but still not quite understand the idea of these two functions.
https://docs.blender.org/manual/en/latest/editors/outliner.html
https://docs.blender.org/manual/en/latest/files/data_blocks.html

1、What’s the different between “Delete”,“Unlink” and “ID data>Delete”,“ID date>Unlink”

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2、If I want to delete an object from the scene, what’s the different between delete it by “Delete” and by “Unlink”?
The ID Data manual said that “To unlink a data-block from its “owner” (e.g. a material from its mesh).” but what if I just unlink a mesh or a linked file? I don’t understand what’s the different between deleting it.

2

ummm…Is there really no one knows the answer or I post on wrong place?

3

Unlink removes data from current owner/user and Delete removes it globally from everywhere even if it is protected (i.e. fake user)

4

Thank you for your reply!
But what’s the different between the one in ID Data and the one outside?

5

Judging by equality of python tooltips, I’d say both Unlinks doing same task. The one outside is likely aimed for unlinking objects from collections (maybe outside submenu for easier access). But I am not sure.

6

I see, thank you!