The mechanism by which a service communicates.
SESAR European ATM Architecture (EATMA) Guidance Material v7 (D138, Ed. 00.07.00, 2016)
Service providers and consumers need to implement Service Interfaces to be able to collaborate. A Service Interface includes service operations that enable access to the functionality of the services identified, as well as the Data Elements used in the service interaction. A Service Interface specifies the Service Interface Definition provided and required by the Service.
Lexicon Release 2015.1