In physics jargon the couple is a pair of anti-parallel forces, of equal magnitude, seperated by a distance.
The torque of a couple is equal to the magnitude of the force(s) multiplied by the seperation distance.
Torque = Fa (Where F is the magnitude of each force, and a is the seperation distance)
A couple is an explicit definition which comes in handy when dealing with torque in static equilibrium! (Eg. An 'L'-Shaped Formula 1 style car jack can be modelled as a couple)