Lung

The lungs are a pair of breathing organs situated within the chest of most humanoids, on either side of the heart. They are connected to the nose and mouth

The lungs are the means by which oxygen is delivered to the blood and carbon dioxide is expelled from it.

Though most humanoids possess lungs, there are variations found between species. In Humans, the right lung is usually slightly larger than the left.

Klingons have three lungs.

Ferengi have upper and lower lungs as opposed to left and right.

Some species even possess genetically modified lungs, such as the Suliban whose lungs were altered to allow them to process atmospheres which would otherwise have been lethal to them.