Pulmonary fibrosis is a condition in which the lungs become scarred over time.[1] Symptoms include shortness of breath, a dry cough, feeling tired, weight loss, and nail clubbing.[1] Complications may include pulmonary hypertension, respiratory failure, pneumothorax, and lung cancer.[2] Causes include environmental pollution, certain medications, connective tissue diseases, infections, and interstitial lung diseases.[1][3][6] However, in most cases the cause is unknown, and termed idiopathic pulmonary fibrosis.[1][3] Diagnosis may be based on symptoms, medical imaging, lung biopsy, and lung function tests.[1]

Reference
Wiki: Lung fibrosis