Server-client components are a py4web extension of the classical vue components. A vue component is client-only: it lives in the browser. A server-client component has a portion in the browser, and one in the server. The server component is in charge of providing the client component with the information it needs, and of storing any information changes coming from the client. The client component is a vue component that displays the interactive component in a browser page.
The code is part of the examples app that comes with py4web.