Source : Free On-Line Dictionary of Computing

drag and drop
     
        A common method for manipulating files (and sometimes text)
        under a {graphical user interface} or {WIMP} environment.  The
        user moves the pointer over an icon representing a file and
        presses a mouse button.  He holds the button down while moving
        the pointer (dragging the file) to another place, usually a
        directory viewer or an icon for some {application program},
        and then releases the button (dropping the file).  The meaning
        of this action can often be modified by holding certain keys
        on the keyboard at the same time.
     
        Some systems also use this technique for objects other than
        files, e.g. portions of text in a {word processor}.
     
        The biggest problem with drag and drop is does it mean "copy"
        or "move"?  The answer to this question is not intuitively
        evident, and there is no consensus for which is the right
        answer.  The same vendor even makes it move in some cases and
        copy in others.  Not being sure whether an operation is copy
        or move will cause you to check very often, perhaps every time
        if you need to be certain.  Mistakes can be costly.  People
        make mistakes all the time with drag and drop.  {Human
        computer interaction} studies show a higher failure rate for
        such operations, but also a higher "forgiveness rate" (users
        think "silly me") than failures with commands (users think
        "stupid machine").  Overall, drag and drop took some 40 times
        longer to do than single-key commands.
     
        [Erik Naggum ]