Daedric is one of the strongest type of equipment known to Nirn. Mortal eyes usually perceive it as black with the occasional shade of red. Various accounts exist on how to craft Daedric but most agree that it is the result of binding of Lorkhan's blood, Ebony, with a Daedra heart. Some also say that it should always be worked on at night, ideally under a new or full moon, but never during an eclipse. A red harvest moon is best. This however is likely a myth as Daedric armor has been successfully created without those conditions being met. 
The appearance of Daedric is described as outlandish or even corrupted. The appearance is said to be because Daedra are only being able to imitate and are unable to create anything new and as a result we see Daedric come in familiar Tamrielic shapes for their armor and weapons that have been exaggerated.