As much of the sonic characteristics of black metal today seem to have been typified by the sound of bands such as Burzum, Darkthrone, and Immortal in the early 1990s, it is easy for some to forget that the term "black metal" had been used for a decade before these Norwegian bands took it to a different level.
One must keep in mind that the term, as any genre or sub-genre tag, is amorphous, not rigid and static, and evolves and adapts over a period of time. In retrospect, the 'black metal' of the 80s is often deemed the "first wave" of black metal, because the term was used more to describe a group of bands with a similarity in imagery and lyrics rather than in clearly defined musical characteristics.
The term black metal was first coined and popularized by Venom with the release of the band's sophomore album in 1982, "Black Metal". Yet Venom was a part of the New Wave of British Heavy Metal, and indeed was a heavy metal band through and through. So how can they also be classified as black metal when they sound so dissimilar to the bands that we refer to as black metal today? See the list for a brief history of the first wave of black metal.