Marlyn is of Welsh origin and means "sea inlet". It is a unisex name, though it's more commonly used for females. The name was popularized by Marlyn Monroe, the iconic American actress and model from the mid-20th century. In its French form, Marilin, it is associated with the writer and philosopher Jean-Jacques Rousseau, who used it as a pseudonym.
"Marlyn was quite popular as a baby girl name in 1946 and again from 1962 to 1963, with a total of 17 girls named Marlyn born during these years."