What do you mean by redox couple ?

A redox couple may be defined as a combination of the oxidised and reduce forms of the same substance taking part in an oxidation or reduction half reactions. A redox couple is usually represented by separating the oxidised form and the reduced form of a vertical line which represents the interface (solid/solution). For example, in a galvanic cell, the two redox couples are represented as Zn²⁺/Zn and Cu²⁺/Cu. In both cases, oxidised form is put before the reduced form.