In jazz, there is a convention that pairs of written beats are not played equally, as the notation isOtherwise understood, but with the first longer than the second and the shorter second note having an accent. Generally the first note of each of these pairs is twice as long as the second, giving a triplet feel.
The swing feeling alters the way two eighth notes on the same beat are played. When the slider is in "No Swing" position, each of the notes corresponds to ½ (50%) and ½ (50%) of the beat. When the slider is in "Triple-feel Swing" position, the duration of the first eighth note will be 2/3 of the beat, and the second eighth note will correspond to the remaining 1/3. By changing the slider, theUser is able to smoothly alter the swing level, changing the duration of the first note of the eighth pair from ½ to 2/3 of the beat.
You can set this option directly in the main tab "Playback":