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).