Short answers, pulled from the story.
The term indie rock first appeared in print on the 15th of January 1983. Roman Kozak wrote an article for Billboard magazine titled Despite Hard Times, Indie Rock Labels Survive to describe a growing trend of successful independent record labels in New York.
The Sex Pistols performed at Manchester's Lesser Free Trade Hall on June 4 and the 20th of July 1976. These concerts inspired the formation of influential groups like Joy Division, Buzzcocks, and the Fall alongside Factory Records.
NME released the C86 compilation cassette in the mid-1980s featuring tracks by Primal Scream, the Pastels, and the Wedding Present. Bob Stanley called it the beginning of indie music in 2006.
In the early 1990s, Nirvana, Pearl Jam, Soundgarden, and Alice in Chains broke into the mainstream from Seattle. The monumental success of these bands brought increased attention to the indie rock scene and made it possible for a niche movement to be co-opted by the mainstream.
Radiohead achieved near-universal critical acclaim with their experimental third album OK Computer released in 1997. This release occurred as post-Britpop took hold within the UK scene following the waning of Britpop towards the end of the decade.