What does melena signify in a medical context?

Melena refers specifically to black, tarry stools that typically indicate the presence of digested blood. This condition usually arises from bleeding in the upper gastrointestinal tract, such as from ulcers, tumors, or other sources of internal bleeding, where the blood is broken down by digestive enzymes and bacteria, resulting in the characteristic dark coloration. Recognizing melena is crucial in a medical context as it often signals a significant health issue that requires prompt investigation and intervention. The other options describe different physiological conditions or symptoms that do not relate to the presence of blood in stool.