Hi, Kim! A presale is something Cathe offers for workout DVDs that are planned but have not been physically completed yet; you are able to purchase the workouts at a significant discount from the retail price that is assigned once the DVDs are actually done.
I've bought almost all of Cathe's complete production series(es?) since The Intensity Series, usually on the first day of presale, and I've never regretted it. The only ones I haven't purchased are the beginner workouts.