This means the process ended in the Ready state instead of one of the final states (Completed, Cancelled, or Compensated). Usually this is because something happened to interrupt the workflow, and usually this is a grid configuration event like a module activation.
When you make a change to your grid, BAO wants to stop all processing to enact the change. This prevent situations where a workflow begins with the grid in one state and ends with the grid in another, mutually-exclusive state. While trying to process the change, BAO will not start any new workflows and it will give already-running workflows 80 seconds to stop. If a workflow is still running after 80 seconds, BAO terminates the workflow and puts it into the Ready state. This is the state jobs have before they start running, so this tells BAO to run the job again as soon as it can. When there are no more running jobs BAO enacts its change, then begins job processing again, including re-running any jobs it put into the Ready state.
This is normal behavior when a user makes grid changes while a workflow is running. If you want to prevent this from happening entirely, only make grid changes when there are no running workflows that will take longer than 80 seconds to complete.