“Anno regni” is a Latin phrase that means “in the year of the reign” in English. It is often used to refer to the number of years a monarch has been on the throne. This phrase is commonly found in official documents such as laws and statutes in the British context and is followed by a numeral to indicate the chronological order of events or laws in a specific reign.
For example, “Anno regni Elizabeth II” would mean “In the year of the reign of Elizabeth II.” Some constitutional monarchies still use regnal years as a way to keep track of the monarch’s reign.