The terms are interchangeable in meaning: Redox = Oxidation-Reduction Potential (ORP). The term Redox is more commonly used for bioprocess applications in Europe and the U.S. The term ORP is more commonly used for industrial chemical process applications in the U.S.
The redox potential of a media is related to the overall availability of electrons in the media, specifically the ratio of positive and negative ions in the solution. Note that redox measurements vary significantly with changing pH.