It's possible you might be thinking of:
* "GR" as an abbreviation for "Government Regulations": This is a common usage, but it doesn't describe a specific form of government.
* "GR" as a specific abbreviation used by a particular country or organization: This is also possible, but you'd need to provide more context.
Please provide more information, such as the context where you saw "GR" or any other clues, so I can help you figure out what it means.