gistfile1.txt

7. Selection and drop registers "*, "+ and "~ 
Use these registers for storing and retrieving the selected text for the GUI.
See |quotestar| and |quoteplus|.  When the clipboard is not available or not
working, the unnamed register is used instead.  For Unix systems the clipboard
is only available when the |+xterm_clipboard| feature is present.  {not in Vi}

Note that there is only a distinction between "* and "+ for X11 systems.  For
an explanation of the difference, see |x11-selection|.  Under MS-Windows, use
of "* and "+ is actually synonymous and refers to the |gui-clipboard|.