Is prog rock genre defined by instrumental sounds?

Prog is based on fusions of styles, approaches and genres, involving a continuous move between formalism and eclecticism. Due to its historical reception, prog's scope is sometimes limited to a stereotype of long solos, overlong albums, fantasy lyrics, grandiose stage sets and costumes, and an obsessive dedication to technical skill. While the genre is often cited for its merging of high culture and low culture, few artists incorporated literal classical themes in their work to any great degree, and only a handful of groups purposely emulated or referenced classical music.

The genre coincided with the new journalistic division between "pop" and "rock" artists that lent generic significance to both terms, as well as an economic boom that allowed record labels to allocate more creative control to their artists. Prog saw a high level of popularity in the mid 1970s, but faded soon after. Conventional wisdom holds that the rise of punk rock caused this, although in reality a number of factors contributed to the decline.^[6] Music critics, who often labelled the concepts as "pretentious" and the sounds as "pompous" and "overblown", tended to be hostile towards the genre or to completely ignore it.^[7] After the late 1970s, progressive rock fragmented in numerous forms; some bands achieved commercial success well into the 1980s, albeit with changed lineups and more compact song structures, and some crossed into symphonic pop, arena rock, or new wave.

Proto-prog is the advanced music that slightly predates the full-fledged prog era. In 1967, "progressive rock" constituted a diversity of loosely associated style codes. The Canterbury scene, originating in the late 1960s, denoted a subset of prog bands who emphasised the use of wind instruments, complex chord changes and long improvisations. Rock in Opposition, from the late 1970s, was more avant-garde, and when combined with the Canterbury style, created avant-prog. In the 1980s, a new subgenre, neo-progressive rock, enjoyed some commercial success, although it was also accused of being derivative and lacking in innovation. Post-progressive draws upon newer developments in popular music and the avant-garde since the mid 1970s.

Yes, and these sounds are produced by instruments called synthesizers and Mellotrons. Unless you like Tool, in which this rule no longer applies.