What is "easterlings"

In the fiction of J. R. R. Tolkien, "Easterling" and "Easterlings" were generic terms for Men who lived in the east of Middle-earth, who mostly fought under Morgoth and Sauron, not directly but rather on behalf of their own lords.

In J. R. R. Tolkien's legendarium, the Easterlings of the First Age were Men who lived in the east of Middle-earth, and mostly fought under Morgoth. They are different from the Easterlings of later Ages.