The Empty Lands were regions in the East of Arda beyond the eastern boundaries of Middle-earth. Along with Belegaer, they were "cast back" at the Changing of the World, "and new lands and seas were made".
Other versions of the legendarium
In their earliest appearance in Tolkien's drafts, the Empty Lands were called the "Barren Land". When Belegaer and the Barren Land were "cast back," the "new lands and seas" were said to appear in areas where previously "nought had been but the paths of the Sun and Moon." In a later draft, "Barren Land" was replaced with "Empty Land," which was eventually replaced with the final term "Empty Lands."