Alternative pop/rock refers to artists that are rooted in the style, sound and/or ethos of punk rock. It is essentially a continuation of the post-punk and new wave genres of the early 80's only even more fractured and diverse. The first wave of alternative rock included jangle pop, grunge, noise rock, and some of the more eclectic punk and hardcore bands. Most alternative rock bands in this wave were largely underground although some became cult hits(Pixies, The Replacements, The Smiths) and a few even gaining mainstream success(U2, R.E.M, The Cure). In 1991 bands like Nirvana, The Red Hot Chili Peppers and Pearl Jam brought alternative to the mainstream.
Even earlier than this late 70's with bands like Talking Heads in the U.S. and Elvis Costello in the U.K. plus Blondie and early U2 were on the cusp of alternative, very much influence. Started getting Radio play, LP/CD sales and video's on the new cable Music Stations. .