What term describes a circumscribed collection of pus surrounded by a wall of inflammatory tissue?

The term that refers to a circumscribed collection of pus surrounded by a wall of inflammatory tissue is “abscess.” An abscess typically forms when the body's immune system responds to an infection, leading to the accumulation of pus, which is made up of dead cells, bacteria, and other debris. This pus is contained within a well-defined area, surrounded by the body’s inflammatory response, which often includes swelling and redness.

In contrast, a cyst is generally a sac-like structure that can be filled with fluid or semisolid material but is not necessarily associated with infection or pus. A fistula is an abnormal connection or passageway that forms between two organs or vessels in the body, often as a result of injury or disease, and does not describe a pus-filled cavity. Hence, the distinct characteristics of an abscess confirm why this is the correct answer.