The Unfan

Its not, its a sub-genre of metal. Ironically NWOBHM isn't a genre as much as a term to describe certain bands from an era who pretty much either played heavy metal or traditional doom in retrospect. What defines "Heavy metal" and "traditional doom" didn't really come about until later but there are obvious differences between bands like Witchfinder General, Pentagram, and Black Sabbath who played heavier slower pieces and Iron Maiden and Judas Priest who played more technical in your face music. The styles the two different breeds of metal would later influence would determine what was what.