There isn’t one. A vicar is a priest who has a specific leadership role in a diocese.
Essentially right, but a vicar could also be a bishop or even a cardinal in a large diocese. The vicar general is the second in command, and in Rome, that could be a cardinal, because the Ordinary of Rome is the Pope, and he has lots of other thing to do.
The judicial vicar is head of the diocesan tribunals, or chief judge under the authority of the bishop.
As a member of a cathedral parish where the bishop is officially the pastor some of our previous rectors served as vicar general, while our current rector is the judicial vicar. Priests who serve in a parish but are not the pastor may be called assistant pastors, but their official title is parochial vicar.
It is also possible for a priest to simply be in residence at a parish and have some other duties, like chaplain at a hospital or for a convent, or high school or college. Our parish has had several priests form African countries in residence while they study at Notre Dame, but help out on weekends.