HMP
noun
Prison;
UK prison, abbreviation for "Her Majesty's Prison" (now "His Majesty's Prison"). Used to refer to the British jail system, often mentioned when talking about being locked up, having people inside, or life in and out of custody.
Prison, coming from “Her Majesty’s Prison” (now “His Majesty’s Prison”). Man might say someone’s in HMP to say they’re locked up, often carrying a serious or cautionary tone about jail time and the system.