empyema

This term is a specialized medical descriptor used primarily in clinical settings, such as radiology reports or surgical notes. It carries a heavy clinical weight, denoting a serious complication rather than a simple infection, and is rarely used in casual conversation outside of a healthcare context.

Because it refers to a specific pathological state of fluid accumulation, it is treated as an uncountable noun in most medical contexts. It describes the condition itself rather than a discrete object that can be counted.