What is the opening of a pore called?

The term that refers to the opening of a pore is known as "ostium" (singular) or "ostia" (plural). In biological contexts, particularly in anatomy and physiology, an ostium describes an opening or entrance to a structure, such as the tiny openings in the skin that allow for the excretion of sweat and the release of oils. This term is particularly relevant when discussing the integumentary system, where various types of glands and follicles interact with the skin's surface.

The other options relate to different aspects of skin anatomy. For instance, a follicle refers to a structure that can house hair or a sebaceous gland and is not specifically about the pore's opening itself. The dermis is the thick layer of skin beneath the epidermis that contains connective tissue, blood vessels, and nerves, whereas the epidermis is the outermost layer of skin. None of these terms accurately describe the specific opening of a pore.