Fusion = a blending of two or more traditional styles of music (rock + jazz). Miles Davis’s “Bitches Brew” from the late 60’s kicked it off. Many bands followed (Weather Report, Tony Williams Lifetime, Mahavishnu Orchestra, etc), but the fad died a slow, quiet death in the mid-1970’s.
Cult = bands (regardless of style) that are hugely popular to a small number of loyal fans. They can be up and coming or of the ‘been around forever and ain’t never gonna make it big’ variety. Some (arguable) cult bands are NRBQ, Grateful Dead, and Fugazi.
Christian Rap = A weird idea if you ask me, but it pretty much is what the name implies. No bitches and ho’s, but lots of Jesus. Most well known is DC Talk.
Tribal = not African music as the name may imply. Tribal is a sub-genre of Electronic/Techno music that’s heavy on percussions.
Electronica = This galls music fans and techno fans. This is a contrived word thought up by the music press to label traditional DJ type-music. The term was coined for umbrella usage when the record labels were thinking that electronic music was gonna be the next grunge ($$$).
Alternative Rock = differs from rock the same way pop does. Only marginally. It was around before grunge, and was a fairly acurate description of some bands (Husker Du, Replacements, early REM), an alternative to the mainstream. Grunge popularized the term, which then meant it was mainstreamed. Now alternitive rock usually means pop/rock band who play commercial music but are (laughably) harder than what you hear on top 40 stations. They are in fact two sides of the same coin (see Blink 182, Len, Green Day).
Noise = really weird atonal noise experements. Whole albums of screeching and clanging. No melody or percievable unifying thread. Lots of avant garde ‘noise’ artists are german and japanese. Go Figure.
Acid Jazz = something akin to blacksploitation music (like the songs Theme from Shaft and Freddy’s Dead). Except there are often no vocals. Really good stuff if you like funky, groove-type stuff. US3 had a top 40 hit about 5-6 years ago called Cantaloop, they are listed under acid jazz fairly often. Pretty poppy example. If you like Issac Hayes or the like, check out this stuff.
Big Beat = pop friendly ‘electronica’. Really catchy stuff. The biggest name in electronica is arguably Fatboy Slim, a practitioner of Big Beat.
Trance = one of my personal favorites. A sub-genre in ‘electronica’. Same groove over and over for a while, then changes for a while, etc. Very hypnotic. Some of the coolest (and most popular) DJ’s in the world practice this type. See John Digweed and/or Sasha.
A quick note to Kyomara. Led Zeppelin aren’t typically thought of as pop because they never aimed for singles chart success and presented their products as “Album Oriented Rock (AOR)”. If you wanted the music you had to buy the records. No singles. (LZ did release one single, Whole Lotta Love and it went to #4 on the pop charts but that was a one off thing). The concept of AOR is still used by radio today, usually classic rock stations are known by that acronym in the biz. But does it really even apply anymore?
Hope this helps. PJ