The document discusses remote procedure calls (RPC) and how they work. It explains that a local function call involves directly calling and returning from the function, while a remote function call serializes the request, sends it over the network to the server, the server then calls the function, serializes the response, and returns it to the client. It provides examples of implementing RPC in Scala using libraries like Airframe that handle the serialization and deserialization of requests and responses.