COPD stands for Chronic Obstructive Pulmonary Disease, also commonly referred to as chronic obstructive lung disease. It is a chronic inflammation of the respiratory tract caused by inhalation of tobacco smoke, other types of smoke, harmful gases, or particulate irritants. This inflammation persists, eventually leading to structural changes in the airways, and symptoms such as coughing up phlegm and difficulty breathing. Chronic bronchitis is diagnosed primarily based on symptoms. Also known as chronic obstructive bronchitis, it is defined by symptoms of coughing, phlegm, or wheezing lasting more than three months per year and persisting for over two years, while excluding other diseases. There is a close connection between chronic bronchitis and COPD. If a patient with chronic bronchitis experiences worsening of their condition characterized by restricted airflow, as identified through pulmonary function tests indicating airflow limitation, they can then be diagnosed with Chronic Obstructive Pulmonary Disease. However, if a patient only exhibits symptoms of chronic bronchitis and maintains normal lung function, they cannot be diagnosed with Chronic Obstructive Pulmonary Disease under such circumstances.