The conventional wisdom is that Glam Rock was a 70s phenomena and Glam Metal an 80s one.
It is well accepted that the first mention of “heavy metal” as it relates to music, was the song “Born To Be Wild” which was a massive hit off Steppenwolf’s self-titled debut album in January 1968. From just about that point in time, hard rocking bands were classified as heavy metal, including Black Sabbath, Deep Purple, Led Zeppelin, Wishbone Ash, UFO & Blue Oyster Cult. The heavy metal designation lasted throughout to the 90s when for these bands, the term “Classic Rock” seemed to be a more appropriate classification as ‘metal’ had gained a new meaning.
From that time, metal splintered off into the emergence of a number of sub-segments including thrash metal, death metal, speed metal, melodic metal and so on. However what these types of ‘metal’ all have in common is that they are a niche and underground movements. With the exception of perhaps Metallica, and possibly to a very limited degree…Pantera, Judas Priest & Iron Maiden, true metal from the 80s, was never a mainstream form of music. It never climbed the popular music charts and it wasn’t until the early 90s with the arrival of the “nu metal” scene which included the likes of Linkin Park, Faith No More & Slipknot etc, that there was mainstream interest in it.