green card: n. [after the "IBM System/360 Reference Data" card] A summary of an assembly language,

:green card: n. [after the "IBM System/360 Reference Data"
card] A summary of an assembly language, even if the color is not
green. Less frequently used now because of the decrease in the use
of assembly language. "I'll go get my green card so I can check
the addressing mode for that instruction." Some green cards are
actually booklets.

The original green card became a yellow card when the System/370
was introduced, and later a yellow booklet. An anecdote from IBM
refers to a scene that took place in a programmers' terminal room
at Yorktown in 1978. A luser overheard one of the programmers ask
another "Do you have a green card?" The other grunted and
passed the first a thick yellow booklet. At this point the luser
turned a delicate shade of olive and rapidly left the room, never
to return..
-- The AI Hackers Dictionary