I have been using these for a long time, and I am hereby stating their definitions so that everybody knows what I am talking about. If these words and phrases already mean in some pop music subculture that I don't know about, then tough. I am going to keep using my definitions, and encourage their use by others.

Pulsebeat

Music where the drum kit consists of only one drum, or the drummer plays the entire kit as if it were one big drum, and most especially where the whole band conspire to play like one massive drum. Note that whether or not the rythym is suggestive of the human heartbeat is irrelevant. Short sections of pulsebeat occur in most genres of rock, but the first and most well-known band to sustain it for entire songs is the Velvet Underground.

Mainline

The main riff of a song. Also as a verb, "to mainline", "mainlining", means to play the main riff.

Dungeon Rock

Hard rock, metal, or prog rock with lyrics that deal with topics from J.R.R. Tolkien or Dungeons and Dragons.

Explicit references to the Judeo-Christian God and/or Devil disqualifies a song as Dungeon Rock, because those were deliberately left out of both Tolkien's work and the original D&D. I suppose some sort of exception might be made for things like King Arthur's quest for the Holy Grail, which is nominally a "Christian" myth but not actually part of the Christian religion. And I guess you can talk about witches, as long as you don't specifically associate them with having sold their souls to Satan, and you don't intend your song to be about Wicca.

Norse myth is OK as long as it is approached from an "adventure" standpoint rather than as part of neo-Pagan spirituality. Ditto for Celtic. Same for Greek myth, if you leave out songs that are really about Jungian psychology and other contexts in which it is obvious that the myths are only being used as symbols to illustrate some intellectual point. Myths of peoples outside of Europe are theoretically fertile ground, but as these are treated in neither Tolkien nor early D&D, there isn't really any excuse for using them in Dungeon Rock.

There are many examples of Dungeon Rock from Led Zeppelin, Rush, (early) Black Sabbath, Rainbow. There are apparently quite a few modern metal- and prog-type bands out that there would fit the bill.

I am not sure if music from other genres counts or not. For example, 60's psychadelic music about elves and fairies; or Goth(ish) music about Vampires.