Psoriasis vulgaris: The medical name for the most common form of psoriasis ("vulgaris" means common). About 80% of people with psoriasis have this type. It is also called plaque psoriasis because of the characteristic plaques on the skin: well-defined plaques of red raised skin that can appear on any area of skin, although the knees, elbows, scalp and trunk are the most common locations. 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.