To me it seems to be settings. But I have seen it been used for more and edit. Or can to gear icon be all three?(or even more?)
A gear icon is more like a settings icon, yep. A edit icon I think a pencil or a paper+pencil is more appropriate.
Just google it "gear icon" and you`ll see a lot of examples, the same with "edit icon".
Well, these two works very fine for me.
Consistency is the key, like our good friend floppy icon.
If your user is used to see the "something icon" like some specific action, be careful if you gonna change it.
On its own the gears icon probably doesn't have the 'edit' or 'more' meanings associated with it compared to 'settings'.
I can see that in the context of some existing fields, the presence of a gears icon (or any other icon) might prompt to the user that you can edit or modify the content by clicking on some link or icon.
Also, if you are already in a settings related window or context, the presence of a gears icon could possibly indicate that there are more settings available if you click on the icon.
However, I don't think I've seen a settings icon that has the popup text of 'edit' or 'more' when you hover over it, so I am curious to see some screenshots and examples that you have mentioned.
I have always seen it associated with settings. Not sure how a gear icon could be used as "more" or "edit"
I would be fairly confident that the gear icon is universal symbol for settings when used as a button.