Plain English Meaning
It is the last day the database provider will accept new chart or procedure information for the next update of the navigation database. Anything that arrives after that day has to wait for the following update.
Full Definition
The published deadline by which a navigation database provider must finalize all source data, procedure changes, and amendments for inclusion in the next AIRAC navigation database cycle. Any change received after the cutoff date is held over for a later cycle.
Context Anchor
Seen in discussions of aircraft navigation databases, instrument procedure data, and how database providers prepare each update.
Derivation
“Cutoff” means a stopping point or limit, and “date” is the calendar day attached to that limit. In this context, it helps you remember that the provider has a fixed day when input for that update stops being accepted.