1. The classification of metals in the order of their electrode potentials.
2. A serial arrangement of metallic elements or ions according to their electrode potentials determined under specified conditions; the order shows the tendency of one metal to reduce the ions of any other metal below it in the series.
3. A series in which the metals and other substances are listed in the order of their chemical reactivity or electrode potentials, the most reactive at the top and the less reactive at the bottom.
4. A tabulation on which various substances; such as, metals or elements, are listed according to their chemical reactivity or standard electrode potential.

It is usually ordered with increasing standard electrode potentials (most negative on top).

For metals, the order indicates the tendency to spontaneously reduce the ions of any other metal below it in the series.

During electrolytic reduction of cations (for example, electroplating) an element lower in the series (more positive) will deposit first, and an element higher in the series (more negative) will deposit only when the solution is practically depleted of the ions of the first element.