BILL—Let’s go to the USDF Glossary of Judging Terms for starters. As is the case with much of our dressage vocabulary, many terms don’t exist in isolation but usually in relation to other ones. CADENCE is defined as “the marked accentuation of the rhythm and emphasized beat that is a result of a steady and suitable tempo harmonizing with a springy impulsion.” [Bold face addition mine] You could imagine it not only visually but aurally—the marked sound of a rhythmical, repetitive drumbeat.
SUSPENSION is “the moment or phase of the trot, canter or passage in which the horse has no feet on the ground.” Basically you can measure it with a ruler or a stop watch. How far off the ground your horse lifts and how long he stays there are directly related—a function of the immutable law of gravity. More suspension will be an increase inn both measures.
Enhanced suspension will heighten the cadence.