This reports the peak-used count of STREAMS message blocks (mblks) (message-block header structures, the basic unit STREAMS uses to pass data between modules) on this host: the highest number of message blocks (mblks) that were concurrently in use at any one time since the subsystem was last initialised. The source MIB's own DESCRIPTION here is only the placeholder "T B S" (to be supplied), so this reading is inferred from the object's name and its position in the same five-column Config/InUse/Used/MaxUsed/Fails pattern that this table documents in full for the streamsStatsQueues* and streamsStatsStreams* resource types earlier in the same table.