The generic term in Roman legal language was rector provinciae, regardless of the specific titles, which also reflects the province's intrinsic and strategic status, and corresponding differences in authority.
To appeal a governor's decision necessitated travelling to Rome and presenting one's case before either the praetor urbanus, or even the Emperor himself, an expensive, and thus rare, process.
An appeal was unlikely to succeed anyway, as a governor wouldn't generally take the chance of convicting someone contrary to the Emperor's wishes.
The governor was also supposed to travel across his province to administer justice in the major towns where his attention was required.
As a part of his standing orders, the governor had the authority to use his legions to stamp out organized criminal gangs or rebels in the area without need for the Emperor's or Senate's approval.
[1] This system, however, started to break down after private citizens were given commands in Spain pro consule during the Second Punic war.
[3] However, the provinces that ex-praetors were assigned – regardless of formal title – were usually the more tranquil ones, where chances of revolt or invasion were small.
A provincial governor almost possessed unlimited authority and often extorted vast amounts of money from the provincial population—but, though he retained immunity from prosecution as long as he held his imperium, once he left office he became vulnerable to prosecution for his actions during his term.
These provinces were away from the Empire's borders and free from the likelihood of rebellion, and so had few, if any, legions stationed in them (thus lessening the chance the Senate might try to seize power from the Emperor).
Augustus decreed that at least ten provinces would be held by the authority of the Roman people through the agency of the Senate.
Diocletian set up twelve dioceses (later several were split), originally two to four for each of the four co-emperors under the short-lived Tetrarchy (two senior Augusti, each above a Caesar), each governed by a vicarius ('vicar') who acted on behalf of the praetorian prefect.
In those provinces where soldiers were stationed, the dux (Latin for leader) commanded border military units.
Constantine, again following Diocletian's lead, organized the Roman Empire into three Praetorian prefectures late in his reign.
These were based on the territories controlled by the four co-emperors of the Tetrarchy, two of whom, the senior Augusti, had been served by a praetorian prefect as something like a chief of staff.