A rotary razor means that it has rotating heads ( i.e. Most Norelco electric razors). They rotate around chopping off hair in a way. They don't cut as close as manually shaving so I don't like them.
A rotary razor is a dry electric razor. You can use some shaving cream with the razor fro a cleaner shave but the razor is made to be used dry. It can be used the same as a regular razor but with a less effort because of the moving blades.
