- An accumulation of air or gas in the pleural space, which may occur spontaneously or as a result of trauma or a pathological process, or be introduced deliberately ( = pneumothorax, artificial). (Dorland, 27th ed)
Definition from: MeSH via Unified Medical Language System at the National Library of Medicine
- A condition in which air or other gas is present in the pleural cavity and which occurs spontaneously as a result of disease or injury of lung tissue, rupture of air-filled pulmonary cysts, or puncture of the chest wall or is induced as a therapeutic measure to collapse the lung.
Definition from: Merriam-Webster's Medical Dictionary by Merriam-Webster Inc.
See also Understanding Medical Terminology.