"An electrode that has a well known and stable equilibrium electrode potential. It is used as a reference point against which the potential of other electrodes (typically that of the working electrode or measuring electrode) can be measured in an electrochemical cell. In principle it can be any electrode fulfilling the above requirements. In practice, there are a few commonly-used (and usually commercially-available) electrode assemblies that have an electrode potential independent of the electrolyte used in the cell. For some common reference electrodes see e.g., the silver/silver-chloride electrode, calomel electrode, and hydrogen electrode. "
A reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant (buffered or saturated) concentrations of each participants of the redox reaction.