Prorogation is a simple and rather dull idea that has suddenly become exciting. A five-year parliament is generally divided into sessions, usually annual. The Queen suspends parliament by proroguing it at the end of each session. The power to decide whether and if so when to prorogue and reopen parliament is part of the royal prerogative. They advise Her Majesty on its use and the constitutional convention is that she must act on their advice.

Source: The Times July 17, 2019 15:56 UTC