3GPP 23.501 v20.2.0 — the document's own text
N.1 General
Taught in 24. Networks that are not for everybody (The 5G system architecture, in depth).
A Localized Service is a service, which is provided at specific/limited area and/or can be bounded in time. The service can be realized via applications (e.g. live or on-demand audio/video stream, electric game, IMS, etc.), or connectivity (e.g. UE to UE, UE to Data Network, etc.).
A Localized Service provider is an application provider or network operator who make their services localized and that are offered to the end user via a network. A network providing Localized Services can be an SNPN or a PNI-NPN.