NOTAM : Notice to Airmen. A notice containing information (not known sufficiently in advance to publicize by other means) concerning the establishment, condition, or change in any component (facility, service, or procedure of, or hazard in the National Airspace System) the timely knowledge of which is essential to personnel concerned with flight operations.
NOTAMs will be in force to keep aircraft away from the upcoming Democratic and Republican conventions. Ignore them and you might just have some company.
(found at at the always excellent PointNiner blog)