The lung is an organ of respiration. The walls of the lungs have capillaries through which blood circulates, allowing for gas exchange; in most humanoids this involves the uptake of oxygen.
The Ferengi have upper and lower lungs.
Lurians have at least four lungs. (DS9: "The Sound of Her Voice")
Klingons have three lungs due to brak'lul. It is believed that the third lung gives warriors extra stamina on the battlefield. (VOY: "Lineage")
Suliban lungs normally have three bronchial lobes, however, the genetically altered Suliban soldiers had five. They also had alveoli clusters, which had been modified to process different kinds of atmosphere. (ENT: "Broken Bow")
Fantome's people had a large lung capacity which allowed them to survive in an oxygen-less atmosphere for an extended period of time. (VOY: "The Void")
The Augments during the Eugenics Wars had lung efficiency that was 50% better than that of a normal Human. (TOS: "Space Seed")
In 2371, both of Neelix's lungs were removed by a group of Vidiians. Unable to create artificial lungs, The Doctor had to use a blood-gas infuser, cytoplasmic stimulator and an isotropic restraint in combination with his newly created holographic organ replacement in order to keep him alive. Later, one of Kes' lungs was altered and transplanted into Neelix by the Vidiians. (VOY: "Phage")
In "The Haunting of Deck Twelve", Tuvok says to Neelix: "
Imagine your lungs filling with oxygen." Tuvok either did not recall that Neelix only had one lung, or he again had two lungs.
In 2372, the alveoli in Tom Paris' lungs began to mutate after he broke the transwarp threshold. (VOY: "Threshold")
Captain Ramirez's lung was punctured during a Cardassian attack on the USS Valiant shortly after the beginning of the Dominion War. (DS9: "Valiant")