Originally a term for the Independent/Unsigned Indie Rock scene, now is a sub-genre of alternative rock. Not only categorized anymore by the Independence or label of the band, but rather by the sound. Vocals usually exemplify attributes such as exadurated consonant pronunciation, Poetic/symbolic/allegoric lyrics, lyrics which are completely random and interpretive, or lyrics that tell a story. The lyrics of certain songs may be confused with "emo" music, but the Indie scene does not center on such pathetic subjects and has an overall brighter philosophy on life. Sloppy guitar chords, random solos, violin/other commonly classical instrumentals, Off-beats and unique digital editing.
I know they're on a major label, but they are definitely Indie Rock!