A made-up music genre created by bored moronic suit and ties at record labels, radio stations, and MTV so that everyone can clamor on to another phony genre.
Bands like Three Doors Down, Hinder, Nickelback, Creed, Saliva, Three Days Grace, Godsmack, etc. all use the word to avoid being called metal, which they really are, but a really bad, sucky dumbed down version of it.
Hinder is not a Post-grunge band, but a hair band without the hair
Godsmack is not a post-grunge band, but a metal band with their instruments tuned down.
Daughty not a post-grunge band, but a Bon Jovi/Nickelback wanna-be.
Nickelback is not a post-grunge band, but a Bon Jovi Wanna-be.
Post-grunge is genre that doesn't exist.