In a chicken, white meat refers to the breast and wings. The legs and thighs of a chicken are dark meat. There is little nutritional difference between these two types of meat.
Muscles that are not regularly or roughly used result in white meat. In chickens, this is meat on the upper part of the chicken. Dark meat is the result of muscles that are used very frequently, such as legs. The reason for the difference is myoglobin, which is a compound that transports oxygen. Muscles that are used more require more oxygen and, therefore, have more myoglobin. The more myoglobin a muscle receives, the darker the meat will be when cooked.