"Heavy metal" is not harder than "metal". "Heavy metal" has two meanings. The original meaning is hard rock with a special emphasis on distorted guitars and str

"Heavy metal" is not harder than "metal". "Heavy metal" has two meanings. The original meaning is hard rock with a special emphasis on distorted guitars and strong rhythms. "Metal" is an abbreviation of "heavy metal" in this sense. But now "heavy metal" has an additional meaning: the traditional 1970s/1980s style of heavy metal, e.g. Black Sabbath, Iron Maiden, Judas Priest. "Heavy metal" in this sense is a sub-genre of "heavy metal" in the previous sense. Most fans of "heavy metal" in the first sense abbreviate it to "metal", and use "heavy metal" specifically for the older style. With these meanings, "metal" includes extreme metal styles, e.g. death/black metal, so it's on average harder than "heavy metal".