Final answer:
A narrow opening or furrow in the skin is called a sulcus or groove. It is formed by an elongated basin or small pit in the skin.
Step-by-step explanation:
A narrow opening or furrow in the skin is called a sulcus or groove. It is formed by an elongated basin or small pit in the skin. This can be seen in various skin conditions like acne and folliculitis where hair follicles become clogged and infected.