According to Wikipedia:

NOTAM or NoTAM is the quasi-acronym for “Notice To Airmen.” NOTAMs are created and transmitted by government agencies and airport operators under guidelines specified by Annex 15: Aeronautical Information Services of the Convention on International Civil Aviation (CICA). A NOTAM is filed with an aviation authority to alert aircraft pilots of any hazards en route or at a specific location. The authority in turn provides a means of disseminating relevant NOTAMs to pilots.

NAVAREAS are the geographic areas in which various governments are responsible for navigation and weather warnings.