Unrest is one of the negatives to public order. But dont think that 'unrest' is the only cause of bad 'public order'. Its just one of several factors.
Unrest is shown as swords crossed over a red flame background and are at the left end of the negative public order. See city detail screen and hover mouse pointer over the icon to see the % effect.
Three main causes of unrest:
- The region has a built in unrest level
- There is an enemy spy in the town
- The city has recently been captured.
This thread started with the observation of unrest type three above. It will wear off ..5% per turn. Whether the unrest completely goes depends on the other two causes.
There might be some ancilleries/traits that cause unrest.