Pulmonary circulation is the half portion of the cardiovascular system which carries Oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

-depleted Blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 away from the heart, to the Lungs, and returns oxygenated (oxygen rich) blood back to the heart. Encyclopedic description and discovery of the pulmonary circulation is widely attributed to Doctor Ibn al-Nafis (1213-1288). The term pulmonary circulation is readily paired and contrasted with the systemic circulation

Systemic circulation

Systemic circulation is the part of the cardiovascular system which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart. This physiologic theory of circulation was first described by William Harvey...

.
A separate system known as the bronchial circulation supplies blood to the tissue of the larger airways of the lung.
Pulmonary circulation is the movement of blood from the heart, to the lungs, and back to the heart again.