It's really just the generic name for all the 35mm Zeiss Ikon Reflex cameras.

If it's an original pre-WWII Contaflex then it's quite desirable and sort after, they were 35mm TLR's and available with an interchangeable f1.5 or f2 Sonnar, or a budget f2.8 Tessar lenses. By chance I have a 1936 BJP Almanac open next to the computer at the review of the Contaflex

Post WWII Contaflex's were a vaied quite varied SLR's, some a lot better than others, overly complex because they used Compur shutters. I think one model took 126 film from memory.

Ian