In the picture, notice the heart-shaped splotch of brightness that helps pollinators such as bees find the blossom's center. This yellow splotch is at the base of an expansive dark-purple petal called a standard . The top petals of all irregular bean-family flowers I can think of are called standards. The standard's name is easy to remember if you know that knights carry their standards high above their heads as they enter battle. The two wings are also typical of bean-family flowers.
Wings are simply the side petals, which sometimes spread away from the blossom like wings.
In Kudzu flowers the keel is so deep and narrow that it practically hides the flowers' stamens, which arch downward inside the almost-shut keel. In fact, the Kudzu's keel has its margins so close together that it's like a pouch with a slit along its top. You can see all this if you study the picture closely. All this strange anatomy instantly makes sense the moment you see a bee land on a Kudzu blossom to do its pollination job. Then the bee goes toward the yellow spot and then upon arrival just reaches up into the keel's interior to get at the nectar.