The word Fusion has been so liberally used since the late '60s that it's become almost meaningless. Fusion's original definition was best: a mixture of jazz improvisation with the power and rhythms of rock. Up until around 1967, the worlds of jazz and rock were nearly completely separate. But as rock became more creative and its musicianship improved, and as some in the jazz world became bored with hard bop and did not want to play strictly avant-garde music, the two different idioms began to trade ideas and occasionally combine forces. By the early '70s, fusion had its own separate identity as a creative jazz style (although snubbed by many purists) and such major groups as Return to Forever, Weather Report, the Mahavishnu Orchestra, and Miles Davis' various bands were playing high-quality fusion that mixed some of the best qualities of jazz and rock. Unfortunately, as it became a money-maker and as rock declined artistically from the mid-'70s on, much of what was labeled fusion was actually a combination of jazz with easy-listening pop music and lightweight R&B. The promise of fusion went unfulfilled to an extent, although it continued to exist in groups such as Tribal Tech and Chick Corea's Elektric Band.