NOTAM
NOTAM or NoTAM is the quasi-acronym for a "Notice To Airmen" at the US Federal Aviation Administration (FAA). A NOTAM is filed with the FAA to alert aircraft pilots of any specific hazards or conditions at a specific location. The FAA in turn reports all relevant NOTAMs to pilots when a pilot files an intended flight plan.
NOTAMs are issued (and reported) due to tower lights being inoperable, for example.