VMS Help TCPIP Services, TELNET, Redefining TN3270 Keyboard, DEF KEY Function  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Use the DEF KEY function to define or redefine a key
    interactively. Your new definition exists until you log out from
    the remote host or disconnect from it.

    When you invoke the DEF KEY function, TN3270 displays a prompt
    in the status line at the bottom of your screen. What you enter
    during the DEF KEY dialog is subject to translation from the
    National Character Set to the DIGITAL Multinational Character
    Set.

    You cannot redefine a key that exists on your National Character
    Set terminal if it lacks a DIGITAL Multinational Character Set
    equivalent.