If you mean a "supercitical wing" it is one which has been designed to give an increased critical mach number.
Critical mach number (MCrit) is the lowest aircraft (freestream) mach number at which the airflow at any point on an aircraft is equal to the local speed of sound (Mach 1). If we confine our considerations to the wings, then MCrit is the lowest mach number at which the airflow over the wings reaches Mach 1.
Air flowing over the wings is accelerated, so its velocity becomes greater than the freestream TAS of the aircraft. When this acceleration plus the freestream TAS equal Mach 1, the aircraft is at its critical mach number. So if we express the acceleration over the wing in terms of mach number, we can say that MCrit is 1 minus the acceleration over the wing. If for example the air accelerates by Mach 0.2 over the wing, then MCrit will be 0.8
In order to increase the speed at which a subsonic aircaft can cruise, the value of MCrit must be increased. To do this it is necessary to reduce the rate of acceleration of the airflow over the wings. This is done by flattening the upper surface to reduce its camber. But this also reduces the lift generated, so supercritical wings also use a reflex camber or concave surface under the rear area of the lower surface.
The reduced camber also permits either a higher MCrit or a thicker wing which makes it easier to support the flight loads. In practice most supercritical wings make a trade off between thicker wings and higher MCrit. So overall supercritical wings tend to be flatter and fatter (thicker) than conventional wings and also have a reflex camber on the lower surface.