COPD 

Chronic obstructive pulmonary disease, or COPD, is a progressive pulmonary illness that can include both emphysema and chronic obstructive bronchitis (and sometimes even asthma depending on the doctor, this is what leads to the confusion). Emphysema is completely different from asthma, it involves damage of the alveoli (little air sacs in the lungs) to the point where they can no longer hold oxygen.

The differences between chronic obstructive bronchitis and asthma are a bit more subtle, however. Though both asthma and chronic bronchitis involve narrowed and and constricted airways, there are a few key differences.

Asthma

With asthma, inflammation is increased upon inhalation of contaminants and it causes the muscle walls to contract around the airway. A fast-acting inhaler works by relaxing these smooth muscles and, in turn, reopening the airways.

Chronic Bronchitis 

Chronic bronchitis is indeed very similar, but it is caused by long term damage to the lungs. This causes the lungs to secrete thicker, heavier mucus and along with the inflamed airways it makes breathing more difficult. With chronic obstructive bronchitis, many patients will develop a thick productive cough as their body attempts to rid itself of the excess mucus.

So as you can see, COPD is a progressive illness that most commonly includes just emphysema and chronic obstructive bronchitis. The latter of these two diseases has similar symptoms to asthma, but different causes and treatments.