MPI Tags

Messages are sent with an accompanying user-defined integer tag, to assist the receiving process in identifying the message.
Messages can be screened at the receiving end by specifying a specific tag, or not screened by specifying MPI_ANY_TAG as the tag in a receive.
Some non-MPI message-passing systems have called tags “message types”. MPI calls them tags to avoid confusion with datatypes.

Messages are sent with an accompanying user-defined integer tag, to assist the receiving process in identifying the message.