Plain English Meaning
A note on the approach chart that tells you this airport cannot be listed as your backup airport on an IFR flight plan.
Full Definition
A symbol shown on an instrument approach chart indicating that the airport may not be filed as an alternate destination on an IFR flight plan, typically because the airport lacks the weather reporting, navigation infrastructure, or approach minimums required to qualify it as an alternate.
Context Anchor
Seen on instrument approach procedure charts and in IFR alternate planning.
Derivation
The letter 'A' refers to alternate, and 'N/A' is the common shorthand for 'not authorized' (sometimes read as 'not applicable'). The symbol with the 'A' inside is the chart convention; 'N/A' next to it tells the alternate is closed for that airport.