Hi, Seabush!
A rotation is a pre-planned sequence of workouts, usually ranging anywhere from 6 to 12 weeks, that is designed to help you meet your specific health/fitness goals (i.e. storage fat loss, muscle mass building, increased endurance, what have you).
Many of the rotations developed by Cathe forum participants incorporate video/DVD workouts other than Cathe's alone, but several of the rotations use hers exclusively. And, rotations can also include non-video/DVD workout bouts (say, running, swimming, fitness walking, free-form weight-lifting).
There has been a recent posting for a collection of rotations that you may want to "sign up" for, if you like the idea of a pre-planned rotation spanning several weeks.
Welcome aboard!
Annette