The word álf (pl. álfar) derives from the same Proto-Indo-European root word from which the Latin albus (white) derives. The original meaning of the word is significant to the character of the álfar of Norse mythology, who retained their light-derived, divine status. Often related or compared to the Vanir (fertility gods) in nature, the elves can be found in association with divinities throughout the Eddas.
The álfar are divided, as are faerie beings in many mythologies, between "Light" and "Darkness," which are often related to the dualistic principle "Good" vs. "Evil," though that is a leap of logic. From the parallelism, though, we derive the two forms of álf: Light (or High) Elves and the Black (or Dark) Elves (compare the Seelie and Unseelie Courts of the Sidhe in Celtic mythology, the Angels and Demons of Christianity, and the Devas and Asuras of Hinduism). Do note that Dark Elves, for being dark and/or light avoiding, are sometimes characterized as evil and so are sometimes maligned, but at the same time are said to aid both Light Elves and the Æsir at Ragnarök.