and someone could argue that a band is a generic term, and then they could argue that a era of a band is generic, and so on.

I heartily disagree. Well, at least in the sense of "generic" that I had set out in the opening post. I think that with virtually all other broad musical super-genres, the music defined under those labels is, at least broadly speaking, significantly more stylistically predictable than the range of music classified as rock. For example - music classified under "rap" will without a doubt have some form of rapping in it. Reggae music will have its regular chops on the back beats. Contemporary R'n'B will invariably use hip-hop inspired beats and be mellow. What I'm getting at is that something in the sound is generally predictable from the broad super-genre label given to a type of music.

But what is predictable from the label "rock"? Very little, in fact probably nothing at all. Rock music needn't necessarily have drums. It needn't have a guitar. It needn't have a bass line. It needn't have a keyboard. Hell, it needn't even have any singing. Of course, it'll have to have ONE of the above, but what sort of a definition is that? "Rock: music that has at least one instrument playing."

I suppose a better question to pose might be: is there anything in music quite so unpredictable from the label alone as "rock"?

Rainard you always post awesome thoughts, it's great!

Lets think about the word 'Rock' for a minute. What does it mean? What does it mean when people yell out "rock and roll"? How about "Rock on"? Or "This rocks!"? It's not defining an instrument is it, it's defining something else, something much less tangible.

Having thought about the origins of the word I think the best way to define rock is about the vibe and feeling of the music. It's about the rhythms and the layout of the piece. When you hear a rock song you aren't listening for a certain instrument, you're listening for that defining sound. Honestly it's a very cheesy definition from me, it's as controversial as when you try to judge the better band based on how much passion they put in, but it's right, no?

Define a "nice day"?

You can't strictly define that using real characteristics such as the sun is shining, it's just something as a person you come to understand the meaning of.

Rock is a Virus
 

Rock music, by its very nature, is in a state of constant flux. It constantly evolves by the combination of various content and musical influences, the constant being the traditional drum, bass, guitar, vocal configuration. Early on, it was the combination of blues, gospel and rockabilly. Lyrical content was sexually based, representing subject matter that was taboo to conservative society of the 50's, creating the rebellious nature of rock n roll. In the early 90's it was Death Metal, suicide, self-mutilation, etc., followed by Nu-Metal which incorporated some of the rap culture. Obviously, there's a commercial appeal to this and record companies quickly figured out how to market the good acts, creating a bunch of imitators, flooding the market with product, desensitizing society to what made the bands sound so dangerous in the first place, making rock music, as you noted, "generic". So like a lethal virus, the next generation of musicians rebel, label the mega-rich rock stars "sellouts" and take the genre to more extreme territory, evolving into a new "strain". All these sub-genres are new strains, and the best ones look to rock society at its core. That being said, rock music seems to be in a slump. Rap music today has become what rock music used to be.

Rock= what we now consider Classic Rock