Server-rendered
Also known as: SSR, server-side rendering
Content that arrives in the HTML the server sends, rather than being assembled by JavaScript after the page loads in a browser.
A server-rendered page contains its own text. A client-rendered one contains a script and an empty container, and the words only exist once the browser has run the script.
Search engines have improved at rendering JavaScript. Most AI retrievers have not, and several do not attempt it at all. They read the response, and if the response is empty, the page is empty.
The test used here is blunt on purpose: at least 250 words of visible text in the raw response. A page that looks full in a browser and returns 40 words to a fetch is not a borderline case, it is a page that most retrieval systems cannot read.
This does not mean abandoning a JavaScript framework. It means rendering the main content on the server, which every serious framework has supported for years.