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 supply oxygen to the bloodstream and remove carbon dioxide. This capacity is often assessed through a test called the diffusing capacity of the lungs for carbon monoxide (DLCO). A lower diffusion capacity can suggest lung diseases, such as chronic obstructive pulmonary disease (COPD) or pulmonary fibrosis, which can impair gas exchange and affect overall health.