In an electrochemical cell, there are at least two (and often more) electrodes which provide a pathway for charge to flow into and out of the cell. This flow of charge through an electrochemical cell causes (or is the result of) oxidation and reduction of various chemical species located within the cell.
In a simple two electrode cell, chemical species are oxidized at one electrode and reduced at the other electrode. The electrode at which oxidation occurs is called the anode, and the electrode at which reduction occurs is called the cathode.
A cathode is an electrode at which reduction is occurring.
In the context of a multielectrode cell or a cell where the direction of the current frequently changes, the terms anode and cathode are less useful. Instead, the terms anodic current or cathodic current are used to indicate whether the process occurring at the electrode is an oxidation or a reduction, respectively.