Plain English Meaning
It means there is no air traffic controller directing the aircraft. Pilots watch out for each other, talk on a shared radio frequency, and follow standard procedures to stay clear of one another.
Full Definition
In aviation, 'uncontrolled' describes airspace or an airport where air traffic control (ATC) does not provide separation services to aircraft. Pilots operating in uncontrolled airspace or at uncontrolled airports are responsible for their own separation from other traffic, using see-and-avoid procedures and standard practices on a common .