"Middle Men" was a term used by the Númenóreans for Men of Middle-earth who were related to the Edain, the ancestors of the Númenóreans themselves. The proper term is "Men of Twilight" (as opposed to the Men of Gondor, "Men of Light", and the Haradrim and Easterlings, "Men of Darkness" etc.). After the founding of the Realms in Exile, Arnor and Gondor, many Middle Men became subjects of the Dúnedain, and eventually intermarried with them until they became one people.