In this series Rich explores the music theory behind jazz guitar improvisation. The series offers you a lot of ideas to help your understand these concepts and how to use them to improvise, to become a better soloist.
JAZZ IMPROVISATION, (a partial description from Wikipedia)Basically, improvisation is composing on the spot, in which a singer or instrumentalist invents solo melodies and lines over top of a chord progression played by rhythm section instruments. Jazz improvisation is distinguished from other genres use of this approach by the high level of chordal complexity, often with one or more chord changes per bar, altered chords, extended chords, augmented chords, and ii-V-I progressions, all of which typically move through multiple keys within a single song. https://en.wikipedia.org/wiki/Jazz_improvisation