Swing is very important in improvisation. This word means stressing the upbeat. If you also give a "sliding" or "retardation" between notes, you can create the real swing jazz rhythm, which was born at the beginning of the XX century about. When you stress an upbeat you make perhaps a "swinging" rhythmics, (also being without a dragging or a sliding between notes), for modern rhythm too, (such as pop and rhythm and blues).