Bebop (or Bop) was developed in the early 1940's and had established itself as vogue by 1945. It's main innovators were alto saxophonist Charlie Parker and trumpeter Dizzy Gillespie.
Until then, Jazz improvisation was derived from the melodic line. Bop soloists engaged in chordal improvisation, often avoiding the melody altogether after the first chorus. Usually under seven pieces, the soloist was free to explore improvised possibilities as long as they fit into the chord structure.
Differing greatly from Swing, Bop divorced itself early-on from dance music, establishing itself as art form but severing its potential commercial value. Ironically, what was once thought of as a radical style, Bebop has become the basis for all the innovations that followed.