How would you define rock music?

Only just seen your question, I've been away awhile. To quote from Ian Kilmister:

Only way to feel the noise is when it's good and loud,
So good you can't believe it's screaming with the crowd,
Don't sweat it, get it back to you,
Overkill, Overkill
On your feet you feel the beat, it goes straight to your spine,
Shake your head you must be dead if it don't make you fly,
Don't sweat it, get it back to you,
Overkill, Overkill
Know your body's made to move, you feel it in your guts
Rock 'n' roll ain't worth the name if it don't make you strut,
Don't sweat it, get it back to you,
Overkill, Overkill

Really difficult one this! I like the definition above, but would welcome something a little more 'scientific'! It should, I feel include a rejection of any music which 'swings'. I love Swing; but it is the antithesis of true 'Rock'. (Some rock music is, of course, very slow and gentle...)

Rock & Roll is often used as a generic term, but its sound is rarely predictable. From the outset, when the early rockers merged country and blues, rock has been defined by its energy, rebellion and catchy hooks, but as the genre aged, it began to shed those very characteristics, placing equal emphasis on craftmanship and pushing the boundaries of the music. As a result, everything from Chuck Berry's pounding, three-chord rockers and the sweet harmonies of the Beatles to the soulful pleas of Otis Redding and the jarring, atonal white noise of Sonic Youth has been categorized as "rock." That's accurate — rock & roll had a specific sound and image for only a handful of years. For most of its life, rock has been fragmented, spinning off new styles and variations every few years, from Brill Building Pop and heavy metal to dance-pop and grunge. And that's only natural for a genre that began its life as a fusion of styles.

That definition will do for me, Roogalator!