Plain English Meaning
It is the reference code for a particular aviation notice, like a tracking number that identifies that one notice out of all the others currently in effect.
Full Definition
A unique identifier assigned to a specific Notice to Air Missions, used to reference, track, and confirm receipt of that notice. The ID typically combines a letter or number sequence with the issuing facility or year, allowing pilots, controllers, and briefers to cite an exact NOTAM without quoting its full text.
Context Anchor
Seen when checking current NOTAMs for airspace activity, including special use airspace that may affect a planned route.
Derivation
NOTAM stands for Notice to Air Missions (formerly Notice to Airmen). 'ID' is short for 'identifier.' Together it simply means the identifier that points to one specific notice.