COPD stands for Chronic Obstructive Pulmonary Disease, commonly referred to as emphysema. This disease describes the irreversible, progressive destruction of those little air sacs in your lungs known as alveoli. This eventually leads to a breakdown in how effectively your lungs can pull oxygen into your bloodstream, while also getting carbon dioxide out. So the lungs are becoming much less efficient at their designed job, which is to get the good air in and the bad air out. The muscles supporting the airways also become floppy in COPD, causing the airways to narrow when you breathe out, causing increased shortness of breath.
The single, largest risk factor for developing COPD is tobacco smoking. COPD is the third leading cause of death in the world and growing. The only way to limit the progressive effects of COPD is to quit smoking.