Atelectasis (pronounced at-uh-LEK-tuh-sis) is the term for a collapse of one or more areas in the lung. When you breathe in, your lungs fill up with air. This air travels to air sacs in your lungs (alveoli), where the oxygen moves into your blood. The blood delivers the oxygen to organs and tissues throughout your body.
https://my.clevelandclinic.org/health/diseases/17699-atelectasis