The current terminal screen height and width are the height and
    width last established by the SET TERMINAL command. By default,
    if you did not enter a SET TERMINAL command, the current height
    and width are the height and width known to the terminal driver,
    as displayed by the DCL command SHOW TERMINAL (usually 24 lines
    and 80 columns for VT-series terminals).

    Related commands:

       SET TERMINAL
       SHOW DISPLAY
       SHOW WINDOW