Start with something you already trust. When your code calls a function like greet("Ada"), the call and the answer happen in one place, in memory — instantly, and all-or-nothing: it either ran and gave you "Hello Ada", or it didn't run at all. Now put the function on ANOTHER machine. Your code still writes greet("Ada"), but the framework quietly turns that line into a network round-trip: a *client* sends a request over the wire, a *server* runs the function body and computes "Hello Ada", and a reply comes back. That trick — making a call to another machine LOOK like an ordinary local function call — is called a **Remote Procedure Call (RPC)**: an RPC is a useful lie, a network round-trip dressed up as a function call. The piece doing the dressing-up is the **stub**: the auto-generated client-side shim that you call like a normal function, which packs your arguments, sends them, and unpacks the reply — so your code never sees the network. Watch the local call first, then the same call as an RPC. Linger on the wire: that gap between request and reply is the whole story.