green bytes

green bytes n.  (also `green words') 1. Meta-information
   embedded in a file, such as the length of the file or its name; as
   opposed to keeping such information in a separate description file
   or record.  The term comes from an IBM user's group meeting
   (ca. 1962) at which these two approaches were being debated and the
   diagram of the file on the blackboard had the `green bytes' drawn
   in green.  2. By extension, the non-data bits in any
   self-describing format.  "A GIF file contains, among other things,
   green bytes describing the packing method for the image." Compare
   {out-of-band}, {zigamorph}, {fence} (sense 1).