meta bit

meta bit n.  The top bit of an 8-bit character, which is on
   in character values 128--255.  Also called {high bit}, {alt
   bit}, or {hobbit}.  Some terminals and consoles (see
   {space-cadet keyboard}) have a META shift key.  Others
   (including, *mirabile dictu*, keyboards on IBM PC-class
   machines) have an ALT key.  See also {bucky bits}.

   Historical note: although in modern usage shaped by a universe of
   8-bit bytes the meta bit is invariably hex 80 (octal 0200), things
   were different on earlier machines with 36-bit words and 9-bit
   bytes.  The MIT and Stanford keyboards (see {space-cadet
   keyboard}) generated hex 100 (octal 400) from their meta keys.