In aqueous solutions, redox potential or oxidation-reduction potential (ORP) is a measure of the tendency of the solution to either gain or lose electrons when it is subjected to change by introduction of a new species.
A solution with a higher (more positive) reduction potential than the new species will have a tendency to gain electrons from the new species (i.e. to be reduced by oxidizing the new species) and a solution with a lower (more negative) reduction potential will have a tendency to lose electrons to the new species (i.e. to be oxidized by reducing the new species).