Plain English Meaning
It is the FAA's official book of instrument approach charts, departure charts, arrival charts, and airport diagrams. When a pilot needs the chart for an instrument approach into an airport, this is where it comes from.
Full Definition
A government publication issued by the FAA that contains the official charts and supporting information for instrument approach procedures, standard instrument departures (SIDs), standard terminal arrivals (STARs), and airport diagrams used in the United States. It is published in regional volumes on a 56-day revision cycle and is the authoritative source for the charts pilots use during operations.