Why is it called "Heavy Metal" music?

Many people attribute it (or at least the term) to a line from Steppenwolf's "Born To Be Wild": I like smoke and lightning Heavy metal thunder Racin' with the wind And the feelin' that I'm under So there's that ;)

Like Ericsson73 says, you've got the Steppenwolf song, and there was also an early review of Jimi Hendrix's music, which describes it as "Heavy Metal falling from the sky"! :)

I think I remember hearing something about the town that Black Sabbath was from, (pretty much the fathers of Metal, unless you count Led Zeppelin, which some do and others don't). I think it was a very industrial town with a lot of factories and things like that and the name "heavy metal" had something to do with how most of the people were employed somewhere that dealt with a lot of literally heavy metal. Also, Iommi (the guitarist from Sabbath, if I'm spelling it right) had his fingertips on one hand cut off in an industrial accident, so he de-tuned his guitar to ease the tension/vibration in the strings and gave their music a "heavier" sound. Without this, they would've sounded less dark than they did and Metal might not be here as we know it today, or at least it would've taken longer to start. Also, I think the term "Heavy Metal" is probably just a way of saying how the music conveys more power and aggression than "rock" music. If rock was somewhat "harder" than the music that preceded it, then what would you call music that's "harder than rock?" I guess you'd call it metal, since that's about as hard as it gets. I dunno, it's just a guess, and I'd go with the Sabbath story as an origin of the term "heavy metal," but I think that some kind of concept similar to this is what probably popularized it at least.

Metal as u know indicates power of music.it is heavy metal because it is the starting of the three metal genre.and there are alot of sub genre's of heavy metal.my favourite heavy metal band is,it actually comes under the sub genre called the "nu metal" "KORN"

In my undestanding it is called Heavy Metal coz it developed a thick, heavy, guitar and drums centered sound.