It is technically a kingdom.
The Monarch is a King or Queen also known as the head of state. (In the UK, Charles III is the current Monarch of the UK since Elizabeth III recently died.)
The next monarch in line is the oldest child of the monarch or the oldest sibling of the monarch. (William is next in line).
There is a few countries who has the UK's monarch as the head of state. they are called Commonwealth countries (Including Canada, Australia, and more).
I don't live in the UK, but that is what I remember. Sorry for wasting your time.
Caption this Meme
