re: What's the difference in "Alternative rock" and "Indie rock" music?

Alternative rock, originally, was simply guitar-bass-drum based music that did not fall in line with the "rock" music being played on the radio. You can go all the way back to the 60's with some of the psychedelic rock that was around that did not make it onto the radio. Then, of course, it comes forward into 70s punk and 80s "new wave" music, and so on.

Indie rock was literally independent music, in the same vein musically as alternative rock, without major label support. Bands that made records through hometown labels and such.

Presently, alternative rock is still new rock that is not considered "hard rock." While indie rock is essentially the same but typically much more experimental and not as radio-friendly (translate: hipster).