An oxidation reduction potential meter, which claims to measure negative ions contained in the human body, was featured on TV. What is oxidation reduction potential?

An oxidation reduction potential meter does not directly measure negative ions contained in the human body. ORP (Oxidation Reduction Potential) shows an electronic energy to oxidize or deoxidize substances. Generally, ORP in alkaline solutions tend to have negative values (mV), which varies depending on the conditions. (It is just for your reference.)