My Two Cents
Hi, Danna. That "rotation" word can be confusing, because I'm sure people use it in different ways. For me, a "rotation" is simply a particular set of tapes I use during a 4-6 week period in order to accomplish a specific goal--or simply to refresh my workout. Setting up a rotation calendar gives me something to look forward to and provides a certain amount of motivation.
For example, I might use Cathe's PS series every other day, alternating with a Cathe step tape, a Christi Taylor hi/lo tape, and a day of jogging outdoors for cardio. After a few weeks, I might switch to FIRM tapes, alternating with an interval tape, a long walk, and a yoga/stretch day. Any change in your workout routine makes your muscles react differently, and helps advance your fitness in a new way.
Cross-training in aerobic conditioning means using a variety of cardio activities: step, hi/lo, running, swimming, walking, biking, Stairmaster. The point is to avoid doing the same thing--whether strength or cardio--over and over for a long period of time. That will diminish your results, and (worst of all) could lead to boredom and burnout.
Hope this helps. Best wishes, Barbara