Thanks for coming to this unusual question. So I was designing a system architecture with microservices architecture. I divided the system into multiple services. Such as Auth, Interaction, etc.
Are they services or microservices or APIs? Obviously, they are accessed by REST API. What should I call them? Auth API or Auth Service?
Also, they talk to each other with gRPC which requires defining the RPCs in a service. What should I call that? Such as AuthDataTransferService or AuthDataTransferAPI??
I am quite a beginner in this field, so sorry in advance for any mistakes in the question.
As the name microservices suggests you divide your application into small, independent services. So, calling your highest level components as services is absolutely a good approach.
Calling them XYZAPI would prevent you from future extensions. Even though your service expose its functionalities today as a REST/gRPC API, it does not mean you don't need to provide a web/mobile UI as well for your future consumers.
Please also note that Auth abbreviation is ambiguous. Did you mean Authentication or Authorization? Former is usually abbreviated as AuthC, whereas latter as AuthZ.