It doesn't have a name per se. It's just called " White Dress of Marilyn Monroe" She wore the dress in the 1955 film The Seven Year Itch. It's a white ivory cocktail dress that was designed by William Travilla
A shame that this particular dress made famous by Maralyn Monroe, never has its own tag
Guessing you're thinking about her dress in The Seven Year Itch, but it's not the same. That was a halterneck gown, longer than the sundress here, that's way shorter, with spaghetti straps and an overlapping fold.