EXCH

   To  exchange  two  things, each for the other; to swap places. If you
   point to two people sitting down and say "Exch!", you are asking them
   to trade places. EXCH, meaning EXCHange, was originally the name of a
   PDP-10  instruction  that  exchanged the contents of a register and a
   memory  location. Many newer hackers are probably thinking instead of
   the  {PostScript}  exchange  operator  (which  is  usually written in
   lowercase).

[glossary]
[Reference(s) to this entry by made by: {PDP-10}]