If you "unpublish" a job, the posting will no longer be active. To reactivate the listing, you will need to either purchase a new job or utilize a new credit from an existing job pack.
If you "hide" your job posting, it will no longer be active or visible to jobseekers – yet you will still have the ability to unhide and re-activate the job to a live posting on the job board.
Not that hidden jobs will still expire after 30 days. If you post a job on January 1st and then hide the job for two weeks in January, the posting will still expire on January 30th.