Mode N is a concept for a ground-based positioning/navigation system (A-PNT) that can supplement GNSS or partially replace it in the event of a failure, while also being more robust against spoofing/jamming. European CNS roadmaps describe Mode N as a "next-generation" ground-based positioning system.

SSR Mode S (Mode Select) allows selective interrogation of an aircraft using a unique 24-bit ICAO address and also supports data transmission (e.g., aircraft identification). ADS-B on 1090 MHz is typically transmitted as "Mode S Extended Squitter."

SSR transponder mode that reports the barometric pressure altitude (typically in 100-ft increments) in addition to the identification code.

SSR transponder mode that transmits only a four-digit identification code (squawk/SSR code) in response to interrogations.

ADS-L (Automatic Dependent Surveillance – Light) refers to a family of light broadcast protocols for electronic conspicuity, in which GNSS-based position/identity data is transmitted over a short range. ADS-L is not identical to ADS-B and is not directly compatible with ADS-B (1090 MHz).

Airspace in which UAS operations are spatially/temporarily separated from other (especially manned) traffic. This can greatly reduce the risk of air collisions (e.g., ARC-a).

Airspace that is reserved for specific purposes, thereby restricting its use by other traffic. In SORA/PDRA, reserved/segregated airspace can be part of air risk mitigation.

Airspace area around an aerodrome with special traffic rules/procedures. For UAS operations, the ATZ environment is particularly relevant in risk assessment (e.g., ARC).

In the SORA context: Area outside a "populated area" and outside the Aerodrome Traffic Zone (ATZ) of an airport.

For SORA/AMC, "populated area" is understood in context as "congested area": an area in a city/town/settlement that is primarily used for residential, commercial, or recreational purposes.