A Marilyn is a hill of any height with a drop of 150 metres or more on all sides. In other words, a relatively high hill. The Marilyns in Britain and the Isle of Man are listed in a book called The Relative Hills of Britain (RHB) by Alan Dawson, published by Cicerone Press in April 1992. Details of subsequent changes have been published in a series of updates.
There are currently 1557 Marilyns. Beinn Dearg near Cape Wrath became the 1557th in July 2018. On 13 October 2014, Rob Woodall and Eddie Dealtry climbed Stac an Armin and then Stac Lee, and so became the first people to climb all the Marilyns. On 17 October 2015 Alan Whatley and Michael Earnshaw became the third and fourth people to climb them all. Six others followed on within a year, making ten Marilynists to date. Anyone who has climbed at least 600 Marilyns is eligible to join the Marilyn Hall of Fame (Marhof), which has over 300 members. To apply, contact the RHB membership secretary Chris Watson by email to firstname.lastname@example.org.
More information about Marilyns is available in these sources: