Dunmer is a race of elves. They are also known as Dark Elves. These two terms mean the same race.
They belong to The Ebonheart Pact so if you chose Dunmer your allies will be Nords and Argonians. Their homeland is Morrowind.
The appearance of the Dunmer race is similar to other elves but Dunmer have red eyes and dark skin. That’s why they are called Dark Elves. If you see an elf with red eyes it is Dunmer. They are rather tall: taller than Bosmer but shorter than Altmer.
They are very strong, quick and have awesome intellect. Such a combination of talents allows them to be good warriors or sorcerers. They like melee hand-to-hand combat and the art of magic. Many awesome warriors and mages can be found among the Dunmer. They are also good assassins and some of them work for the Dark Brotherhood.