VMS Help SET, TERMINAL, Qualifiers, /TYPE_AHEAD  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /TYPE_AHEAD (default)
       /NOTYPE_AHEAD

    Controls whether the terminal accepts unsolicited input to the
    limit of the type-ahead buffer.

    When you specify the /NOTYPE_AHEAD qualifier, the terminal
    accepts input only when a program or the system issues a read
    to the terminal, such as for user input at the DCL prompt ($).
    When you specify the /TYPE_AHEAD qualifier, the amount of data
    that can be accepted is governed by the size of the type-ahead
    buffer. That size is determined by system generation parameters.