User created content is just that: content that is created by someone who plays the game. Another phrase for it is "3rd Party Custom Content."
And I don't think deleting it won't screw your game up. Since I doubt that console versions of the game have cache files, you can probably do it without having to do anything else. However, if you've used it in your game and a sim is in the process of using this particular item, I can't say how the game will react when you load the save. Most likely, it will replace the item with something that does the same thing, and/or the sim will simply cancel the action. But really, I have no way to know for sure, as I didn't even know that console players had access to custom content.
