Chronic obstructive pulmonary disease (often called "COPD") is a condition in which the airways in the lungs become inflamed and narrowed (chronic bronchitis) and the air sacs become damaged (emphysema).
Cigarette smoking is the most common cause of COPD. As the lungs become more damaged over time, it becomes increasingly difficult to breathe. When the damage is extensive, it may also become harder for the lungs to get enough oxygen into the blood and to get rid of excess carbon dioxide. These changes all lead to shortness of breath and other symptoms.
Treatment of COPD can often help control shortness of breath and cough and can sometimes slow the progression of the disease. But the most important thing you can do to improve how you feel is to stop smoking and avoid breathing smoke.