Wiktionary
n. (context derogatory English) A kind of music snobbery that views rock music as normative and values music with "authentic" production values over modern "manufactured" and electronic forms.
Wikipedia
Rockism is a pejorative term referring to perceived biases in popular music criticism. The fundamental tenet of what is considered "rockism" is that some forms of popular music, and some musical artists, are more authentic than others. The term rockism was coined by Pete Wylie in 1981 with his Race Against Rockism campaign. It was used humorously by certain critics in the British music press from the early 1980s to express "violently pro-pop" principles.
Rockism, derived from this original usage, can be defined in more than one way, and it would be difficult to recognize one absolute meaning. While there are many vague interpretations of it, rockism is essentially believed to treat rock music as normative. From a rockist view, rock is the standard state of popular music.
Despite the name, it is not rockist to like rock music, or to write about it. One may also care about R&B, Electronic music, Folk music, Jazz, Classical Music, norteƱo or bubblegum pop, but discuss them in a rockist way. The idea is built into the way people talk informally about what kinds of popular music interest them. For example, when talking about Jazz, a rockist is likely to praise Miles Davis, John Coltrane, or Charles Mingus, because their music was marketed by way of "cohesive studio albums" (i.e. Kind of Blue, A Love Supreme, and The Black Saint and the Sinner Lady). However, when it comes to artists like Louis Armstrong, Duke Ellington, or Charlie Parker, these artists reached their prime before studio albums were a common commercial practice. So, becoming familiar with their work in the present day would require hunting down singles, live albums, or compilations, all of which are formats rockists view as being inferior. So, a rockist would likely ignore these artists, despite the fact that in non-rockist jazz circles, Armstrong, Ellington, and Parker would be viewed as being just as important as Davis, Coltrane, or Mingus.
It is also possible to criticize rock music in a rockist way, such as dismissing a rock band because a writer feels as though they have no good albums and only solid singles, or that they have a high abundance of cover songs in their catalog and thus are not "real musicians" (e.g. The Byrds and Led Zeppelin).
Design critic and indie pop musician Nick Currie (aka Momus) compared Rockism to the international art movement Stuckism, which holds that artists who do not paint or sculpt are not artists.