Diffusion capacity refers to the ability of the lungs to transfer gases, such as oxygen and carbon dioxide, between the air in the alveoli and the blood in the capillaries. It is an important measure of lung function, indicating how effectively the lungs can facilitate gas exchange. This capacity is often assessed through a test called the DLCO (Diffusing Capacity of the Lung for Carbon Monoxide), which measures how well carbon monoxide can pass from the lungs into the bloodstream. A lower diffusion capacity can indicate various lung conditions, such as pulmonary fibrosis or emphysema.