An uncontrolled decompression is an undesired drop in the pressure of a sealed system, such as a pressurised aircraft cabin or hyperbaric chamber, that typically results from human error, structural failure, or impact, causing the pressurised vessel to vent into its surroundings or fail to pressurize at all.
In aviation, uncontrolled airspace is airspace in which an Air Traffic Control service is not deemed necessary or cannot be provided for practical reasons.