COPD: Chronic obstructive pulmonary disease. Any disorder that persistently obstructs bronchial airflow. COPD mainly involves two related diseases -- chronic bronchitis and emphysema. Both cause chronic obstruction of air flowing through the airways and in and out 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.

COPD is also called chronic obstructive lung disease (COLD).