(1) A data set on disk storage that contains queues of messages awaiting transmission to particular terminal operators or to the host system.
(2) In PSF, a virtual data set built by the library access system interface (LASI) subcomponent in memory to store error messages for printing at the end of the document.
(3) The message data set is used principally to pass messages about the current state of specific resources from the active system to the alternate system. It is also used for the secondary surveillance signals of the active, alternate, or both CICS systems, when the control data set is unavailable for this purpose, either because the last write has not completed yet or because of I/O errors.