Men (initially named Atani) were one of several races inhabiting Arda. They are the humans of Middle-earth, and the second of the Children of Ilúvatar.
The race of Men was the second significant race of beings created by the supreme God, Ilúvatar, since they awoke in Hildórien at the start of the First Age, at the first rising of the Sun (FA 1), while the Elves awoke three Ages before them. They were called the "Afterborn" (Quenya Atani, Sindarin: Edain) by the Elves.
Men bear the Gift of Men, which is mortality, and therefore they age and die when their time comes, and are susceptible to illness and disease. Elves are immortal, in the sense that they are not susceptible to aging and disease. Even the Valar did not know what ultimate fate awaited the souls of Men, as this was known only to Eru.