1. Deterioration or damage in metals caused by oxidation or chemical action that is caused or accelerated by an electrochemical cell.
2. Electrochemical corrosion associated with the current in a galvanic cell, caused by dissimilar metals in an electrolyte because of the difference in potential (emf) of the two metals.

The abbreviation emf refers to "electromotive force" or the cell voltage of a galvanic cell measured when there is no current flowing through the cell.

In other words, the equilibrium electrode potential difference between the two electrodes of the cell.