Uh. I actually have no idea why it's there. Lol
Last time I had one I disappeared on me.
Ah, here we go.
A Dormant Bounty is when you die with a bounty on your head, but not within the jurisdiction of the issuing faction.
So, if you're getting annoyed by dormant bounties. Stop dying.
I believe they expire after a certain time, or you can get them reactivated with a scan from the issuing faction, and then wait them out again, then pay off the fine.