A CPAP (Continuous Positive Airway Pressure) machine is a medical device used primarily to treat obstructive sleep apnea (OSA). OSA is a sleep disorder that causes a person's breathing to stop and start repeatedly during sleep, which can lead to oxygen deprivation, poor sleep quality, and other health problems.

The CPAP machine works by providing a constant stream of air through a mask that is worn over the nose or nose and mouth while sleeping. The air pressure keeps the airway open, preventing the collapse of soft tissues in the throat that causes snoring and apnea episodes.

CPAP machines are available in different models and features, but they all work by delivering air pressure at a constant level that is prescribed by a doctor or sleep specialist based on a person's specific needs. Some machines also have additional features such as ramping, which gradually increases the air pressure as a person falls asleep, or humidification, which adds moisture to the air to prevent dryness in the airways.

Overall, CPAP therapy is considered a highly effective treatment for OSA and can significantly improve a person's sleep quality, daytime alertness, and overall health.