Any music that was produced using predictable assembly line style power-chord structures and lyrics with absolutely zero forethought other than rhyme and easy mass-identification. If a band churns out more than one album per year, odds are favorable that they are a butt rock band. Bonus points if the lead singer attempts to emulate Scott Stapp because although Creed is not (quite) butt rock, there would be no butt rock without them. Pioneers of butt rock include Nickelback, Puddle of Mudd, Three Days Grace, Buck Cherry, and Hinder. The song "The New Sh!t" from Marylin Manson's "Golden Age of Grotesque" album can be interpereted as a poignant critique of butt rock.
It only took me one listen to completely digest that new Hinder tune. Butt rock goes down so smooth! I don't have to think at all!