In my early years of jazz listening at the end of the fifties, the word "modern" featured as a jazz category and was used by record stores, etc., along with "traditional" and "mainstream", the latter denoting jazz by musicians of Buck Clayton's generation. Some record stores also had a "progressive" category, which seemed to consist of discs by Kenton and Shorty Rogers. All this, of course, was before the category "avant garde" emerged. Biggest sellers in the "modern jazz" category were Brubeck and the MJQ. In Britain these subdivisions were reinforced by a virtual war between "traddies" and "modernists".