Final answer:
Melena refers to the passage of dark, tarry stools caused by bleeding in the upper gastrointestinal tract. It is important to seek medical attention as it can indicate a serious underlying condition.
Step-by-step explanation:
The condition the 66-year-old female is describing is melena. Melena refers to the passage of dark, tarry stools that are usually caused by bleeding in the upper gastrointestinal tract, such as the stomach or small intestine. The black color is due to the partial digestion of blood in the digestive system, resulting in the release of iron in the form of hemosiderin. It is important for the patient to seek medical attention as melena can be a sign of a serious underlying condition.