COPD: Chronic obstructive pulmonary disease. Any disorder that persistently obstructs bronchial airflow. COPD is frequently related to cigarette smoking and mainly involves two related diseases -- chronic bronchitis and emphysema. Both are frequently present and cause chronic obstruction of airflow obstruction of the lungs. The obstruction is generally permanent and progresses (becomes worse) over time.
Asthma is also a pulmonary disease in which there is obstruction to the flow of air out of the lungs, but the obstruction is usually reversible and between attacks of asthma the flow of air through the airways is usually good.