Daedra (Aldmeri - "not our ancestors") are powerful divine beings from the realm of Oblivion in the Elder Scrolls franchise. Unlike their opposites, the Aedra, daedra did not participate in the creation of Mundus, thus retaining their full power. Daedra are often referred to as demons, but this is misleading. All Daedra have a penchant for extremes and are therefore capable of tremendous acts of devastation, but their different spheres make them apply their power in different ways, and their infinite diversity makes speaking about them generally difficult. Thus, it is often impossible to accurately label them as "good" or "evil"; the one thing that can be stated with certainty is the Daedra are beyond mortal comprehension (as mortals seem to be beyond Daedric comprehension). Daedra are commonly split into two specific types - "true daedra," which refers to the highly intelligent Dremora and Daedric Princes, and the much more common "lesser daedra," which includes all other forms of daedra.
Technically, only the plural is written "Daedra", but this word is frequently used in singular as well. The proper singular form is "Daedroth", but that has come to refer to a specific species of Daedra. Different cultures have their own myths and names for Daedra. For instance, the Khajiit rarely speak of the "Dro-m'Athra", dark spirits that are believed to be Daedra by another name.
A Daedroth's physical form can be slain, but it cannot be truly killed; the soul or Animus of a slain Daedroth returns to the void of Oblivion until it manages to coalesce into a physical form again. A slain Daedroth is often said to have been "banished" or "purged" instead of "killed" to reflect this. Daedra are the undisputed masters of craftsmanship, creating seemingly indestructible armours and the mightiest of weapons through dark rituals. Daedric weaponry is said to be forged from the highest quality of raw ebony. The objects get their power from a Daedric soul forged into the ebony.