Plain English Meaning
The chunk of sky around a navigation station where its signal is officially strong enough to trust. Stay inside that chunk and the navaid works reliably; go outside it and the signal may be weak, unreliable, or unusable.
Full Definition
The defined reception limits of a VOR, VORTAC, TACAN, or NDB navigation aid, expressed as a volume of airspace in which the signal is reliable for navigation. Each class of navaid (Terminal, Low, or High) has a published SSV specifying the range and altitudes within which adequate signal coverage is guaranteed, absent any published restrictions.
Context Anchor
Seen in instrument navigation discussions when describing how far and how high a radio navigation signal can be used reliably.
Derivation
"Service volume" comes from "service" (the navaid serving usable signal) and "volume" (a three-dimensional region of airspace). "Standard" means it is the published, default coverage for that class of navaid — not a custom or restricted one. Together: the standard three-dimensional region in which the navaid's service is guaranteed.
Why Pilots Care
Pilots use it to confirm a navigation aid will deliver dependable guidance at their planned altitude and distance.
Analogy
Think of it like the expected coverage area for a radio station. Inside the coverage area, reception should be dependable; outside it, you might still hear the station, but you should not count on it.
Intuition Check
Do not read volume as loudness here. In this term, volume means a block of airspace where the navigation signal is intended to be dependable.
Example Sentence 1
The instructor pointed out that the VOR they planned to use was a Terminal class, so its standard service volume only extended 25 nautical miles from the station.
Example Sentence 2
Outside the standard service volume the signal may weaken even if the aid is still transmitting.