'Dark Elves' can be used to refer to the Theological standpoint, or to refer to the Dark Elven race, mostly descended from the Illythiri, known to have become the Drow.
Darkened Elves driven underground by the Sundering, this is a theological classification of the Elves who did not take of Evron's corruption to become of the Drow, but still follow Lolthiriel.
The Drow, the chosen race of Lolth, an adapted racial variant of Elf that are now a Younger race.
There are many myths written on the creation of the Dark Elves and the Drow
This definition of 'Dark Elf' is usually, mostly correctly, used to include the Drow as it was from the Dark Elves they were created, however the Drow are still considered a completely separate race.
The Dark Elves, comprised of clans belonging to the Illythiri , the Aqualari and the Miyeritari bloodlines.
They are of the same race as their kin but were regarded to have fallen to the darkness in the Reverie after the death of Lolthiriel and the Sundering, they are forever apart from the others of their race, following their own path of Incantation and Ancestral worship.
The vast majority of the Dark Elves were from the Illythiri blood line lead by Lothiriel herself, and as such the term is interchangeable with the Elves who live in the Underdark.
It should be noted that the "Dark elves" maintained and used a form of Elven runic writing often called Dark elven.
In the years of darkness that followed, brother turned on sister and father on son, mother on daughter. Lines drawn along belief and faith; one side believing that the Darker Elf path was correct and that the Reverie should not be abandoned; the other that the Reverie should be abandoned, along with its corruption. - The Fall of Lolthiriel by Larethian Thuleandor, translated by Ilharess Eld'fein
Clans of the Dark Elves
The Illythiri Clans:
The Miyeritari Clans:
The Aquillari Clans: