Butt rock refers to one of two styles of music depending on era. In the 80s, butt rock referred to hair metal and hard rock bands. Users of the label believed these bands were not adding anything new to the genre. Examples of such bands include Poison, Warrant, and Winger. Though this could be considered "cock rock" because of the sex, drugs, rock 'n' roll aesthetic and lyricism.

Butt rock also and usually refers to alternative rock/hard rock/post-grunge bands in the 2000s. Like with the 80s hair metal, music critics label these bands because they believe that they too are not adding anything new. Examples of these bands include Creed, Nickelback, and Seether.

This tag is very subjective and really does not describe a band's sound though you can infer in it's 2nd use case it's describing rock bands that focus on melodramatic vocal hooks or certain vocal enunciation on top of catchy and punchy guitar riffs.