Post-grunge is an offshoot of grunge that has a less abrasive or intense tone than traditional grunge. Originally, the term was used derisively and indicated mid-1990s alternative rock bands such as Bush, Candlebox, Collective Soul, Live, Foo Fighters, and Silverchair, that emulated the original sound of grunge.

In the late 1990s, post-grunge became a more clearly defined style that combined the sound and aesthetic of grunge with more commercially accessible songwriting, rising to prominence that lasted into the 2000s. Bands such as Foo Fighters, Creed, Matchbox Twenty, Puddle of Mudd, Nickelback, Seether, Staind, Three Days Grace, Breaking Benjamin, and Shinedown achieved mainstream success in this second wave.

During the 1990s, a post-grunge sound emerged that emulated the attitudes and music of grunge, particularly its thick, distorted guitars, but with a less intense and less abrasive tone. Unlike a lot of early grunge bands, post-grunge bands often worked through major record labels. Post-grunge music tends to be in mid-tempo and is noted for having "a polished, radio-ready production", oftentimes with pop song structures, and incorporated influences from other genres such as classic rock, pop rock, alternative metal, and nu metal. Tim Grierson of About.com wrote that musically, post-grunge bands "split the difference between plaintive ballads and aggressive rockers, resulting in songs that combine the two extremes into a sad-eyed, propulsive middle ground". On some occasions, post-grunge music features both an electric guitar and an acoustic guitar playing simultaneously. Post-grunge tends to have production quality that is much higher and cleaner than grunge. Hence, Graham Hartmann of Metal Injection noted that the genre's second wave "had a vice grip on rock radio from the mid-to-late 2000s—arguably the last time a wave of rock experienced mainstream popularity."

A "major rift" between grunge and post-grunge is in the lyrical substance of the music; grunge often expressed emotion through loose metaphors or third-person narratives, while post-grunge was known for being direct and blunt. While describing lyrics that are common in post-grunge, Sasha Geffen of Consequence of Sound wrote that post-grunge "plunged directly into the 'I.' " Geffen also wrote that most post-grunge songs that achieved mainstream success "call after a prospective or past companion in the first person". Post-grunge lyrics also tend to be about topics such as relationships, romance and drug addiction. According to Geffen, "grunge's frontmen posed with their addictions; post-grunge's songwriters sought redemption for them". Geffen then states that post-grunge songs "fit the mold of songs made for ... teenage boys and girls" who were "longing for a distant someone".

Originally, post-grunge was a label that was meant to be almost pejorative, suggesting that grunge bands labelled as post-grunge were simply musically derivative, or a cynical response to an "authentic" rock movement. When grunge became a mainstream genre because of bands such as Nirvana and Pearl Jam, record labels started signing bands that sounded similar to these bands' sonic identities. Bands labeled as post-grunge that emerged when grunge was mainstream such as Bush, Candlebox and Collective Soul are all noted for emulating the sound of bands that launched grunge into the mainstream. According to Tim Grierson of About.com, the almost pejorative use of the "post-grunge" label to describe these bands was "suggesting that rather than being a musical movement in their own right, they were just a calculated, cynical response to a legitimate stylistic shift in rock music". In the late 1990s, post-grunge morphed, becoming a derivative of grunge that combined characteristics of grunge with a more commercially accessible tone. During this time, post-grunge bands such as Creed and Nickelback emerged. Grierson wrote:

Creed and Nickelback espoused a more conventional, almost conservative worldview built around the comforts of community and romantic relationships. Ironically, this attitude was diametrically opposed to the antisocial angst of the original grunge bands, who railed against conformity and instead explored troubling issues such as suicide, societal hypocrisy and drug addiction.

Grierson also wrote, "Post-grunge was a profitable musical style, but bands like Nirvana and Pearl Jam were beloved partly because of their perceived integrity in avoiding the mainstream. Post-grunge, by comparison, seemed to exist in order to court that very audience."

In the 2010s, the derogatory term "butt rock", which had previously been used to refer to glam metal and hard rock acts from the 1980s such as Mötley Crüe, Def Leppard, and Poison, gained traction when applied in relation to many post-grunge artists. Notably, the term would be used to refer to the likes of Nickelback, Creed, Puddle of Mudd, Shinedown, Flyleaf and Hinder. Graham Hartmann of Metal Injection stated that the term "usually refers to the second wave of post-grunge music, where bands like Bush and Candlebox ultimately turned into Nickelback and Seether."