The Tridion 2013 SP1 documentation describes
Copy item link to clipboard as a Content Manager Explorer ribbon command with this description:
Put a link to the currently selected item in the list, or the item currently open in this dialog, in your clipboard so that you can paste it in another application or document.
(source: SDL Live Content)
This also appears in the 2011 documentation.
Which tab should this appear in and when does it apply?