It's a board game.
One board game that starts with "m' is Monopoly.
My Guess would be Monopoly, the real-estate business game.
Monopoly, Maj jong, Mario Brothers video games, Mouse Trap, Mother May I, Madden video games
Mayfair is the most expensive property in British Monopoly.
if you meant the most valuable property it is Mayfair the value goes up in order of position on board e.g. Old Kent road is the least valuable and is at the beginning and Mayfair is most valuable and at the end.
Mayfair (not Mayfair Street) then Regent Street & finally Trafalgar Square.
Very much outdated but £400.
The most expensive property on the UK Edition of Monopoly is Mayfair, costing £400