magic cookie

magic cookie n.  [UNIX] 1. Something passed between routines
   or programs that enables the receiver to perform some operation; a
   capability ticket or opaque identifier.  Especially used of small
   data objects that contain data encoded in a strange or
   intrinsically machine-dependent way.  E.g., on non-UNIX OSes with a
   non-byte-stream model of files, the result of `ftell(3)' may
   be a magic cookie rather than a byte offset; it can be passed to
   `fseek(3)', but not operated on in any meaningful way.  The
   phrase `it hands you a magic cookie' means it returns a result
   whose contents are not defined but which can be passed back to the
   same or some other program later.  2. An in-band code for changing
   graphic rendition (e.g., inverse video or underlining) or
   performing other control functions (see also {cookie}).  Some
   older terminals would leave a blank on the screen corresponding to
   mode-change magic cookies; this was also called a {glitch} (or
   occasionally a `turd'; compare {mouse droppings}).  See also
   {cookie}.