Musicologist Barry Kernfeld wrote in The New Grove Dictionary of Music and Musicians that post-bop is "a vague term, used either stylistically or chronologically (with divergent results) to describe any continuation or amalgamation of bop, modal jazz, and free jazz; its meaning sometimes extends into swing and earlier styles or into fusion and third-world styles.
[2] Jazz historian Stuart Nicholson wrote that "The term post-bop is a wonderful catch-all, used not so much to describe what a style of music is, but more what it isn't.
[1] One potential definition of post-bop is a musical period in which modern jazz was at its greatest mainstream popularity extending from the mid-1950s through to the mid-1960s.
[6] He wrote in his definition of the subgenre: Forms, tempos, and meters are freer, all the compositions are new, and the band members themselves are featured composers.... [A]n approach that is abstract and intense in the extreme, with space created for rhythmic and coloristic independence of the drummer—an approach that incorporated modal and chordal harmonies, flexible form, structured choruses, melodic variation, and free improvisation.
His second quintet was active during 1964 to 1968 and featured pianist Herbie Hancock, bassist Ron Carter, saxophonist Wayne Shorter, and drummer Tony Williams.