Normal skin has balanced levels of moisture and oil. It looks soft, moist and has a healthy glow and colour. It has a fine texture and there are no open pores or fine lines caused by dehydration. The best example is the skin in children. Older people who once had oily skin may also have it (the amount of oil produced by glands has slowed down and the skin has become normal) however, the difference with normal, younger skin is that the muscle tone and colour have deteriorated.
Even if it is balanced, normal skin needs care. Its balance can be harmed by dehydration, bad diet, the use of harsh products, sun exposure, etc. It needs cleansing morning and evening, good moisturisers for day (with SPF) and night and exfoliating occasionally to keep the luminosity and texture.