Today’s Aeronautical Terms

Direct routes, based on area navigation capability, between waypoints defined in terms of latitude/longitude coordinates, degree-distance fixes, or offsets from established routes/airways at a specified distance and direction.
[Source: Instrument Flying Handbook]

Used by ATC to inform an aircraft to turn-off the automatic altitude reporting feature of its transponder. It is issued when the verbally reported altitude varies 300 feet or more from the automatic altitude report.
[Source: Pilot/Controller Glossary]

Either True Course or Magnetic Course.
[Source: Pilot/Controller Glossary]

A general term used to describe airspace in which approach control service or airport traffic control service is provided.
[Source: Pilot/Controller Glossary]

Minimum Descent Altitude
[Source: Aeronautical Information Manual]

Visibility. The ability, as determined by atmospheric conditions and expressed in units of distance, to see and identify prominent unlighted objects by day and prominent lighted objects by night.
[Source: Air Traffic Control System Command Center]