At a guess its how a process (Event Server) balances the workload so that every waiting event (timed/triggered) is processed in the correct/fair order given the available resources.
For example if you dumped 1000 files in a watched directory how many will it process simulaneously, in what order does it choose them fro processing, what priority do the files take over other adapters.
these are all tunable to an extent via the dstx.ini and .msl
Tim