Yass (jass) is a Polish music style of avant-garde jazz which originated in the late 1980s, that mixes jazz, improvised music, punk rock, and folk. The style began with avant-garde jazz musicians from the Tricity and Bydgoszcz, where the jazz club Mózg became the unofficial 'home venue' for Yass performers, with its own label releasing a number of Yass productions.
The term Yass was coined by bassist and guitarist , clarinetist Mazzoll and guitarist , who wanted to stress the novelty of the new style. The first Yass album is generally regarded to be Taà Âce bydgoskie by .
Though it frequently crosses genres, Yass music can be broadly described as a frequently arrhythmic and highly improvised style of jazz. The most seminal period for Yass was in the 1990s, with many active groups performing and releasing albums, including Mià Âoà ÂÃÂ, à Âoskot, Trytony, and Mazzoll & Arhythmic Perfection. A good overview of the Yass scene exists on the compilation album Caà Ây ten Yass! released by Jazz Forum magazine shortly after the genre's heyday.