What is Rock-n-Roll??
Rock-n-Roll started out as a black euphemism for satisfying vigorous sex in the boogie woogie and jazz songs on the 1920's and 1930's. It was a way to say out loud, directly into the face of authority, what you wanted and how you intended to get it without the understanding entirely what the hell you were talking about.
In the 1950's rock-n-roll became a catch phrase that symbolized the solidarity and rebellion of America's first pre-dominantly teenaged society. The music was a blend of rhythm and blues, country western, folk, gospel, jazz, and barbershop harmoniesthat sought to liberate the spirits of its devotees by cathartically enacting scenarios of tension and release within the confines of a 45 rpm pop single.
By the mid 1960's rock-n-roll gave way to rock a music which only had echoes of mutual ancestry in common with the music that came before it. Rock in the late 60's was more divisive, less a shedding of innocence, and the music spoke to the concerns of that generation's youth in that generation's language.
Since those times, music industry flirtations with such diverse musical styles as reggae, disco, new wave, punk, rap, etc.. have spoke the credo of what has come before - "this is our music, you're not supposed to like it!", but they never quite crystalized into the universal voices of their times the way rock-n-roll did in previous incarnations.
These days record company execx label as "Rock-n-Roll" just about any product they want the public to percieve as honest, uncomprisin or fun; regardless of whether said product is rock-n-roll or not, and I for one wish to hell they would stop it!
Rock's next direction? I don't know about you, but I'm all for returning it to being a hip euphemism for satisfying vigorous sex. No less an authority than Elvis Presley once said "I don't play music. I play Rock-n-Roll," which neatly encapsulates my long held theory that rock-n-roll is less a justifiable art form than it is a feeling or an attitude.

To demonstrate, below are some highly subjective (US!) examples of what rock-n-roll is, and by counterpoint, what it is not.

Mexican food is rock-n-roll. Chinese is not.
1966 Mustangs are rock-n-roll. 1986 Mustangs are not.
Mike Royko is rock-n-roll. Russel Baker is not.
The CIA is rock-n-roll. The FBI is not.
Gibson and Martin guitars are rock-n-roll. Ovations are not.
Chicago is rock-n-roll. New York is not.
Waitresses are rock-n-roll. Hostesses are not.
Frankie Laine is rock-n-roll. Jerry Vale is not.
Gorillas are rock-n-roll. Chimpanzees are not.
Hobnobs are rock-n-roll. Rich Tea are not.
Women body builders are rock-n-roll. Women wrestlers are not.
Labador retrievers are rock-n-roll. Poodles are not.
Dwight Yokum is rock-n-roll. Steve Earle is not.
Francis Ford Coppola is rock-n-roll. Martin Scorsese is not.
JFK was rock-n-roll. LBJ was not.
Oysters are rock-n-roll. Clams are not.
Nancy Sinatra is rock-n-roll. Petula Clark is not.
Cloud bursts are rock-n-roll. Drizzling rain is not.
Firesign Theatre is rock-n-roll. Duck Breath Mystery Theatre is not.
Cheeseburgers are rock-n-roll. Yuppie burger bars are not.
"Goldmine Magazine" is rock-n-roll. "Rolling Stone" is not.
Living is rock-n-roll. Dying is not.