The Dúnedain (singular: Dúnadan) were the Humans descended from the Númenóreans who survived the fall of their island kingdom (Númenor) and came to Eriador in Middle-earth, led at first by Elendil and his sons. They are also called the Men of the West and the Men of Westernesse (direct translations of the Sindarin term).
Direct descendants of the Dúnedain are known to live three times longer than normal Humans. The average lifespan for the Dúnedain was between 150-170 years, given normal human lifespan of 50-60 years. At the beginning of the Fourth Age, the blood of the Dúnedain was renewed by Aragorn and Arwen's marriage and many generations thereafter would experience longer lifetimes (possibly between 400 and 500 years).
The Westron name for Dúnadan was simply Adûn, "westerner", but this name was seldom used. This name was reserved to those Númenóreans who were friendly to the Elves: the other, hostile survivors of the Downfall were known as the Black Númenóreans.