When we talk about server-side rendering of websites, we are generally referring to an application or website that uses a programming language that runs on a server. On this server, the web pages are created (rendered) and the output of that rendering (the HTML) is sent to the browser, where it can be displayed directly.

When we talk about client-side rendering, we are generally referring to an application or website that uses JavaScript running in the browser to display (render) the pages. There is often a single page that is downloaded, with a JavaScript file that builds up the actual page (hence the term single-page application).