Diamond wing or Trapezoidal wing configuration is a wing planform that resembles a form of trapezoid with very little sweep. As the name suggest it is of the form of a trapezoid shape with 2 parallel edges and 2 unparallel edge. One of the 2 parallel edges is generally the fuselage.

It is generally used in aircraft incorporating stealth. As a trapezoid has 2 parallel edge, it helps to reduce the radar reflection. The best examples are Sukhoi T-50 PAKFA, F-22A RAPTOR and F-35 LIGHTNING II.
These three 5th generation fighters have almost similar trapezoid shaped wing planform. Most trapezoidal shaped winged aircraft are from United States.
Ex-F-104 starfighter, F-22A raptor, F-35 Lightning II, X-3 Stiletto, YF-23, X-7

Generally these types of wing planform are very thin to get a perfect coat of RAM and also not to disturb the parallel edge by increasing the thickness of the wing. This reduces the air drag at higher mach thus giving the aircraft the ability to supercruise, and that is the case with F-22A RAPTOR. Raptor can go supersonic without engaging the afterburners whereas most swept wing aircraft can’t supercruise without installing a engine with wet thrust having above 150KN.

Trapezoidal wing has almost zero sweep as the both unparalled edges have a resultant sweep of zero. Also it provide a better handling at subsonic speed than other delta wing aircrafts, which makes it suitable for ground attack aircraft too.

LIMITATION:
-As Trapezoidal wings are very thin, they’ve very low loading capacity. So most of them doesn’t have hardpoints more than 8. That is why Raptors are often not prefered for ground attack role and carrier all ammunition in internal bay.
-Because of almost zero sweep, i.e. Due to the fact the the leading edge sweeps backward whereas trailing edge sweeps forward, it kills a bit of maneuvering capability of aircraft at subsonic speed making it less agile than Swept wing or Delta wing in a dogfight.
-Due to the small size of wing, it doesn’t generate enough lift during takeoff. But this problem is compensated by a powerful engine.