A moment is the product of a single force about a point. E.g. when you push down on the end of a wheel brace on a nut on a car wheel.
A couple is two forces acting together, and the magnitude is the torque.
In the wheel brace example, the force produces both a couple (whose magnitude is the torque) and a force at the nut (which pushes the nut).
In a sense, they are the same, but there are subtle differences.
Have a look at this discussion: