Dark Elves
One of the standard elf varieties. They tend to have most (if not all) of the following characteristics:
- Dark-grey skin and white hair
- Overtly supremacist ideology
- An economic system based on slavery
- A system of promotion based on social Darwinism (i.e. killing one's superiors to take their position)
- A fondness for spikes in everything, from fashion to architecture
- Underground dwellings
- A BDSM theme
Dungeons and Dragons
In the various Dungeons and Dragons games (and their spin-offs, like Pathfinder), Dark Elves are usually known as Drow.
Warhammer Fantasy
In the long past of the Warhammer Fantasy world, the Dark Elves were once just elves. Then, heir-apparent Malekith found himself passed over when it came time to choose the Phoenix King, and he started a civil war. When he lost, he and his followers (called the druchii in their language) were exiled across the ocean.
Presently, the Dark Elves inhabit and dominate Naggaroth, the Warhammer World's analogue to North America; this might tell you something on how GW views the Colonies. Their population is concentrated in six major cities, including the capital city of Naggarond, but they also inhabit massive city-ships known as Black Arks, kept afloat by the magic of the Witch-King. Where the arks go reaving, things burn, slaves are taken, and fat lewt is piled high and sent back to Tortureonto (Karond Kar) or Evil Fredericton (Har Ganeth) or Hellifax (Clar Karond) or whatever. Don't fuck with the corsairs.
Then we have the shades, a bunch of hosers that live in the wilderness full of beasts that Chaos dragons think twice before fucking with.
The Dark Elves are also the biggest dicks in the universe- The War of the Beard? oh we raided the dwarven caravans that started it all!' *Mad cackle* "JUST AS PLANNED!"
Males are forbidden to use magic since Malkeith's mum Morathi said that he would one day be killed by one. Not like anyone cares, but it's probably a plot by her to take the throne.
Among their traits are that their nobles ride exothermic carnivorous reptiles into battle. This is weird since their homeland is quite chilly, so you would think that they would be sluggish and inefficient mounts.
Warhammer 40,000
In Games Workshop's quest to give every WFHB race a counterpart in the grim, dark future, they created the Dark Eldar -- all the hedonistic fun of the Dark Elves, but in space!