Client-side rendered pages (aka client-side rendering, CSR, SPA) are pages that are rendered only on the client-side. In other words, all the page's UI components are loaded and executed only on the client-side and never on the server-side.
See API > ssr
for configuring which of your pages should be rendered on the client-side and/or server-side.
See SPA vs SSR (and more) for a guide on whether to choose client-side and/or serve-side rendering.