Indie typically applies to rock music that is outside of the rock mainstream and is not affiliated with a major record label, hence "independent." Some indie groups actually enjoy significant followings and critical acclaim. Music blogs such as Stereogum and Indie Rock Cafe focus on this genre along with "alternative" rock and other emerging rock music.
Indie (independent) films (see In Bruges) and fashions are two other areas where the term is relatively commonplace. The indie tag has further spread to include almost any creative or artistic endeavor that lacks an affiliation with a major brand or label.