Pleural effusion is a medical condition where excess fluid accumulates in the space between the lungs and the chest wall, known as the pleural cavity. This buildup can cause difficulty in breathing, chest pain, and coughing. It often results from underlying issues such as pneumonia, heart failure, or cancer. Doctors diagnose pleural effusion through physical exams and imaging tests like chest X-rays or ultrasounds. Treatment may involve draining the fluid with a procedure called thoracentesis or addressing the underlying cause. Early detection and management are crucial for improving symptoms and overall health.