Here's a breakdown:

* Pus: A thick, yellowish-white fluid composed of dead white blood cells, bacteria, and tissue debris. It's a sign of infection.

* Body cavity: A space within the body that contains organs. Examples include the chest cavity (containing the lungs and heart), abdominal cavity (containing the stomach, intestines, liver, etc.), and pelvic cavity (containing the bladder, uterus, and rectum).

When pus accumulates in a body cavity, it can lead to serious complications if not treated promptly.