What is the term for the collapse of the lung or part of the lung?

The collapse of the lung or part of the lung is referred to as atelectasis. This condition occurs when the alveoli, which are the tiny air sacs in the lungs, become deflated or filled with fluid, resulting in reduced gas exchange and potentially leading to respiratory issues. Atelectasis can develop due to various factors, including obstruction of the airways, pleural effusion, or pressure from outside the lung, among others. It is important to differentiate this term from others related to lung function, as atelectasis specifically indicates the absence of air in the lung's alveolar spaces, marking a distinct pathology compared to conditions like pneumothorax, which involves air in the pleural space causing lung collapse for different reasons.