The Free On-line Dictionary of Computing (30 December 2018):

tn3270

   A program, similar to telnet, used to connect to remote
   IBM mainframe hosts, many of which do not understand
   telnet.  The program emulates a 3270-type terminal.

   For many tn3270 versions, the "clear screen" function is
   activated by typing Control-Z.  When logged on to an IBM host
   and "HOLDING" or "MORE..."  appears at the lower right corner
   of the screen, the "clear screen" function must be entered to
   display the next screen.  tn3270 emulations usually include
   function key definitions.

   (1994-11-03)