chronic obstructive lung disease Any disorder that persistently obstructs bronchial airflow. Abbreviated COLD. COLD mainly involves two related diseases: chronic bronchitis and emphysema. The obstruction is generally permanent and worsens over time. In asthma, there is also obstruction of airflow out of the lungs, but the obstruction is usually reversible, and between asthma attacks, the flow of air through the airways is generally good. Also known as chronic obstructive pulmonary disease (COPD).