AIRAC - Aeronautical Information Regulation And Control
An AIRAC system defines a series of common dates and an associated standard aeronautical information publication procedure for States so that, for both efficiency and safety, Pilots, Air Traffic Controllers, Air Traffic Flow Managers, Flight Management Systems and Aviation Charts all are working from the same information base.
In short it defines that in all instances, information provided under the AIRAC system shall be distributed by the AIS unit at least 42 days in advance of the effective date with the objective of reaching recipients at least 28 days in advance of the effective date. Whenever major changes are planned and where additional notice is desirable and practicable, a publication date of at least 56 days in advance of the effective date should be used.
The concern changes are: airspace structures and routes revisions, navigation aids changes, SIDs and STARs amendments, runway and taxiway information changes.
AIRAC page at ICAO website.