Chronic Obstructive Pulmonary Disease (COPD) describes a group of lung conditions (diseases) that make it difficult to empty the air out of the lungs. This difficulty can lead to shortness of breath (also called breathlessness) or the feeling of being tired.

COPD is a term that is used to describe chronic bronchitis, emphysema or a combination of these two conditions.

1. Chronic bronchitis is an inflammation of airways accompanied by coughing and spitting up of thick sputum (phlegm). In chronic bronchitis, these symptoms are present for at least three months in each of two years. 
          
2. Emphysema is a chronic respiratory disease where there is an abnormal increase in the size of the air sacs in the lungs, causing a decrease in the lungs ability to work correctly, and often, breathlessness. 

NOTE:  COPD is different from asthma, but it can be difficult to distinguish between COPD and chronic asthma.

Source:  VA/DoD Clinical Practice Guidelines