Indie stems from the word independent. The music isn’t attached to a major record label so there is some purity. It’s not about selling a product; it’s about producing good songs. Labels like Matador, Subpop, Saddlecreek Records, and Dfarecords are just a few choice examples of independent music producers. Notable bands include: Interpol, Belle & Sebastian, Bright Eyes, The Rapture, Broken Social Scene, Arcade Fire, Bloc Party, The Shins, Rilo Kiley, PJ Harvey, and Elliot Smith. In general, Indie followers love obscurity. Indie music has also evolved into an entire subculture of “hipsters,” a group of people who listen to Indie music, and have no tolerance for poseurs and the main stream. The lines between indie and mainstream music is really not clear and often a subject of debate.
Please keep in mind, some bands that have spent most of their careers on major labels are still occasionally referred to by the press as indie rock because of their sound or aesthetic, such as Radiohead.
A variety of musical genres and subgenres with varying degrees of overlap are associated with indie rock. Some of these include lo-fi, post-rock, sadcore, C86, math rock, shoegaze/dream pop, indie pop, noise rock, noise pop, riot grrrl, post-hardcore, twee pop, alt-country, post-punk revival, garage rock revival, dance-punk, indie folk, baroque pop, new prog, and indietronica.
The roots of modern indie rock are often traced back to The Velvet Underground‘s self-titled debut album, released in 1967, which was ranked #7 on Blender’s list of the 100 greatest indie rock albums. Allmusic notes that every “left-of-center rock movement owes an audible debt” to this album. The Beach Boys‘ 1966 album Pet Sounds is also commonly listed as a highly influential starting point. Later, the punk movement of the 1970s had a direct impact on the DIY aesthetic that later became a cornerstone of indie rock.
sources: wikipedia, paly voice.net