The Settings -> Job Statuses area allows you to set up your own sub status for each main status to add more information to each stage of the job. The list of Job Statuses appear showing the number of open jobs under each status.
Clicking on the arrow next to any status will display a sub-list of Job Sub Statuses. From here you can select Add Job Sub Status to create a new sub status for that particular main job status.
This will create a row where you can input the Job Sub Status name and Update to save.
You can also Edit or Delete the sub status from the list once it has been created: