Contrary to about 400 of the definitions already listed here, Heavy Metal has nothing to do with Marilyn Manson. Heavy Metal is a genre of music inspired by American Blues music, in which people began to exploit the characteristics of the electric guitar to create louder, more discordant sounds. Heavy Metal is characterized by fast tempo, agressive rythm, and grandoise lyrics, often involving such themes as drug abuse, death, or political issues.
Megadeth, Metallica, Judas Priest = Metal
Marilyn manson, Linkin Park, rapcore music = Not Metal