What term describes a closed sac that contains pus, semifluid, or morbid matter beneath the skin?

The correct term that describes a closed sac containing pus, semifluid, or morbid matter beneath the skin is a cyst and tubercle. In dermatological terms, a cyst is a membranous sac that can be filled with various substances, including fluid, pus, or cellular material. A tubercle is a small, rounded bump on the skin, which can also be associated with a buildup of tissue or pus.

This term encompasses a range of skin conditions where there is an accumulation of substances in a closed space, which is vital for understanding the various dermatological conditions that can occur. Knowing this distinction is important for identifying and treating skin ailments appropriately.