Pleural effusion is a medical condition where excess fluid accumulates in the pleural space, the area between the lungs and the chest wall. This fluid buildup can cause difficulty in breathing, chest pain, and coughing. It can result from various causes, including infections, heart failure, or cancer. Diagnosis typically involves imaging tests like chest X-rays or ultrasound, and treatment may include draining the fluid through a procedure called thoracentesis. Addressing the underlying cause is also essential for effective management of pleural effusion.