A human lung refers to one of the two organs in the respiratory system that are responsible for extracting oxygen from the air and expelling carbon dioxide. The lungs are located within the chest cavity, with one on the left side and one on the right side of the body. They contain millions of tiny air sacs called alveoli, which is where gas exchange occurs between inhaled oxygen and exhaled carbon dioxide. In summary, a human lung refers to an organ that plays a crucial role in maintaining life by providing oxygen for cells throughout the body while removing waste gases.