Indeed there may not be. You do not require server-grade hardware to build a function-as-a-service platform. Moreover you do not need a client-server endpoint

Indeed there may not be. You do not require server-grade hardware to build a function-as-a-service platform. Moreover you do not need a client-server endpoint. If you do have either of those things, it's an implementation detail. Case in point, AWS Lambda was launched without one of them. If you have a better suggestion for a catchy name for function-as-a-service, the world of tech marketing awaits you.