Empyema is defined as what?

Empyema is defined as the presence of pus in the pleural cavity, which is the space between the lungs and the chest wall. This condition often arises as a complication of pneumonia, chest surgery, or other infections that lead to the accumulation of infected fluid in the pleural space. The pus in the pleural cavity can cause significant inflammation and may result in respiratory distress, necessitating medical intervention.

The other options describe different conditions but do not accurately capture the definition of empyema. Fluid build-up in the lungs could refer to pleural effusion, which is the accumulation of fluid without the infectious component that characterizes empyema. A malfunction of the respiratory system is a broad term that encompasses many potential issues but doesn't specifically relate to empyema. Air trapped in the pleural space describes a condition known as pneumothorax, which is distinct from empyema as it involves air rather than fluid.