As is customary in this day and age, we start by going straight to Wikipedia. The world's go-to source for, well, everything tells us that "classic rock" is a radio format that evolved from the "album-oriented rock" or "AOR" radio format in the 1980s, which sounds about right, so long as you know your pop music and radio history. If you don't, you're probably still in the dark.
Without looking at Wikipedia, I will try to communicate my own understanding of what AOR was (and is). Prior to the 1970s -- prior, basically, to the Beatles and the cohort of acts that trailed in their wake -- pop music was almost exclusively a singles game. You cut a track, you released it to radio and onto a small piece of vinyl that people could put on their record players at home, people bought it and/or heard it, and you went on to the next one. Long-play records with multiple tracks on them starting coming out in the 1950s, but most popular acts didn't really make much use of them. They were seen either as repositories for after-the-fact compilations of singles that had outlived their original popularity (i.e. "Greatest Hits" collections), or just a bigger, more expensive version of the single itself (i.e. one song, maybe two if you were lucky, that had had some real care put into it, and then a bunch of crap to fill up the space).
The Beatles changed all that. While their first albums adhered to the formula, as they moved into the middle of their career arc (I'm thinking of "Revolver" and "Rubber Soul", here) they started filling up their albums not just with hit singles but with other songs of equal merit that were nevertheless not cut as singles or sent immediately to radio stations. Eventually they started putting out records like "Sgt. Pepper's Lonely Hearts Club Band" and "Magical Mystery Tour", which have been touted as the first "concept albums". They really weren't true "concept albums" (which I define as a suite of songs that are interrelated in subject matter and/or musical content, meant to be taken as a unified whole rather than as individual songs) -- but the songs on these albums were more related to each other than to anything else the Beatles had done, and not just in terms of style.
Musicologists and historians of music, if you're reading this, just stop. I'm an amateur and I know it.
In any case, once musicians had discovered the potential of long-play albums -- i.e., that you could put a whole bunch of halfway decent tracks on them and make them as valuable as singles -- it set up a dichotomy between "singles" acts and everyone else. "Singles" acts kept to the old pattern of recording a song or two that was worth a damn and would make a ton of money in sales and radio play, and then filling up their albums with a bunch of crap. The proper term for the crap, still used today, is "filler". Everyone else started retreating to recording studios for ever-longer periods of time, often for months, racking their artistic brains until they had a set of good songs ("good" being a highly subjective term, of course) that could fill up a long-play 33 rpm vinyl record.
AOR stations, as the name implies, heavily favored this latter type of artist. But this doesn't get us any closer to a useful definition of "classic rock", now does it?
A list of AOR artists is perhaps more informative. They included: Led Zeppelin, Pink Floyd, The Who (from "Tommy" onward, anyway), Lynyrd Skynyrd, Bob Seger, Bruce Springsteen, Yes, Peter Frampton, ZZ Top, Queen, Rush, Eric Clapton (in all of his incarnations), Boston, Bad Company, Jimi Hendrix, The Guess Who, The Eagles, Thin Lizzy, Foghat and Kansas.
Assuming you know any of those acts, you now have a better idea, no?
That list, as (I hope) we shall see in the near future, is hardly all-inclusive, but it's a start. So what does it show? A lot of white guys, for one. No women to speak of. Now that I mention it, we could add Heart and early Pat Benatar to the list, if we really wanted to, but they're still exceptions to the rule. Jimi Hendrix stands out as a token black. But note that while black artists are rare on the "classic rock" format, nearly all of the acts who make the list practice some form of blues-based rock. They come to music, first and foremost, with an appreciation of black music. What comes out is "blues-rock" or "Southern rock" or even "prog rock", which is another way of saying that black music has been strained through a dense filter of white sensibilities, but this is really the common thread of "classic rock". This is something I will (hopefully) go into with more detail in the future.
As I go through various acts and add them to the "canon" of classic rock, I suppose I should have some criteria. Based on the list above, and the description before it, here's a rough baseline set:
1. "Classic rock" generally refers to music recorded sometime in the interval between the late 1960s (the onset of album-oriented rock music) and the early 1980s (the advent of MTV). Anything recorded earlier could be a precursor to "classic rock" but probably wasn't true "classic rock". Anything recorded afterward that sounds like "classic rock" probably did so intentionally, whether to adhere to the now-established format or as a reaction to other sorts of pop music that had appeared in the interim (such as "New Wave" and synth-pop, to take two examples of genres reviled by many "classic rockers").
2. "Classic rock" is just that -- rock. It is "popular music", but it isn't "pop". It will usually be heavy on the electric guitars and light on the keyboards. It will most often have one foot squarely in the blues. It will go especially well with beat-up old Camaros, dirty white t-shirts, canned, watery American beer, and smoke-filled bowling alleys.
3. Most classic rock acts did not record singles. They recorded albums, and if singles were to be involved, they were chosen after the fact.
I am sure other criteria will emerge as this goes on, but that's a start. Now, on to our first act...
