what is alternative?

[agentfuschia]

how could you distinguish an alternative band or song?

[PonyOne]

That's a tough one; i think everyone has their own idea of what alternative is. Literally speaking, it's whatever is non-mainstream. But then there's the whole issue of what is mainstream.

My band classifies itself as "alternative." We play rock that is not screaming death hard but also isn't like REM. We have a few songs that are yelling distortion fests and some that are very low key sounding, which i think fits the "alternative" genre.

I think that probably the model archetype of alternative is the band Failure: they're a trio (sometimes quartet) from LA that was influenced heavily by 70's and 80's metal but was one of the early 90's revolt bands along with Nirvana, Alice In Chains, Faith No More and to a lesser extent Pearl Jam, albeit a MUCH lesser known band than any of those.
I'd advise you to buy a Failure CD or download some MP3's; if you get a CD get Comfort. You can find some sound clips on CDnow, or go to http://www.geocities.com/sunsetstrip/vine/4999/index.html I'd actually be interested to know what you think of them.