Final answer:
A sinus/fistula is an abnormal connection or passageway that forms between two organs or structures in the body. In dermatology, it refers to a long, narrow channel that develops under the skin due to various conditions, such as infections or injuries.
Step-by-step explanation:
A sinus/fistula is an abnormal connection or passageway that forms between two organs or structures in the body. In dermatology, a sinus/fistula refers to a long, narrow channel that develops under the skin due to various conditions, such as infections or injuries. It usually appears as a small hole or opening on the surface of the skin, and it can be associated with symptoms like drainage, pain, or inflammation.