RPC is an abbreviation for “Remote Procedure Call”. It is an API style for distributed systems. It has been around since the 1980s. Today the most widely used RPC styles are JSON-RPC and XML-RPC. Even SOAP can be considered to follow an RPC architectural style.
The central concept in RPC is the procedure. The procedures do not need to run on the local machine, but they can run on a remote machine within the distributed system. When using an RPC framework, calling a remote procedure should be as simple as calling a local procedure.