There was time when “alternative” and “indie” were synonyms, both words referring to the sorts of music that weren’t likely to spend much (or any) time on the pop charts, both words referencing music made outside of the big industry label machines. But those days are long since gone, rendered ancient history by (in rough chronological order) the ascension of college rock, the breakthrough of grunge, and the strip-malling of radio stations and record labels alike.
So these days “alternative” generally means the sorts of things you’re likely to hear on edgier modern rock radio stations today, and “indie” generally means the sorts of things you’re likely to hear on edgier modern rock radio stations tomorrow. The true alternatives and the real indies of our era are typically the artists who aggressively embrace non-radio and non-chain store distribution methodologies, moving product over the Internet, at DIY concerts, and through word of mouth between like-minded listeners, huddled in an underground deeper than corporate rock’s drills can cut. So far, anyway.