What musical qualities distinguish Rock music from other genres of music?

I don't know that there are any individual traits that uniquely identify rock music. Similarly, I'm guessing that for every trait that we identify as "characteristic of rock music" my guess is that we can find rock songs that don't contain that feature.

That said, we can probably come up with a suite of characteristics that are true to MOST rock songs.

Let's see here:

* Electric guitar is the primary instrument for melody, and often for rhythm.

* Rhythm is typically provided by an electric bass and drums. The beat is typically very strong and clear.

* In its simplest form, it tends toward a 4/4 time signature, though this can vary widely, particularly in progressive rock music.

* There is typically a single lead vocalist who usually acts as the front man, or face, of the band. Other members of the band may sometimes harmonize or sing backup.

* Musical themes tend to focus on concepts that appeal to youth and rebellion, though this is far from universal.

* Musical roots are most clearly tied to blues, but with influences also coming from country and western.

Certainly not a complete list, but maybe that'll get some discussion going.

Overdriven electric guitars, bass guitars, and standard rock drum kits (hi hat, snare, bass drum, three or four toms, three cymbals, occasionally a cowbell or other rmiscellaneous items).