Psoriasis, plaque: The most common form of psoriasis -- about 80% of people with psoriasis have this type. Plaque psoriasis can appear on any skin surface, although the knees, elbows, scalp, and trunk are the most common locations. It is characterized by well-defined plaques of red raised skin. The flaky silvery white buildup on top of the plaques is called scale; it is composed of dead skin cells. This scale comes loose and sheds constantly from the plaques. Skin symptoms include pain, itching and cracking. The technical name for plaque psoriasis is psoriasis vulgaris (vulgaris means common).