What is sub-system name

Where your workflow system only has a single sub-system then the name will likely just be identical to the workflow system name.

Where you have multiple sub-systems then you should give each a unique name to identify them. Many widgets and reports (such as the jobs held widget, upcoming target widget etc) will report upon each sub-job and so they will need a name to identify them individually.

For example in a two sub-system workflow for Year End accounts and Corporate tax -> you would name them accordingly so that you can clearly see which sub-job you are holding.