Simplify the following text for a Grade 9 native English-speaking person.
Original: A Marilyn is a mountain or hill in the United Kingdom , Ireland or Isle of Man with a relative height of at least 150 metres ( 492 ft ) , regardless of absolute height or other merit .
Simplified: A Marilyn is a mountain or hill in the British Isles ( including Ireland ) with a relative height of at least 150 metres ( 492 ft ) .