SPA

A Single Page Application loads one HTML page and dynamically updates content as the user interacts, without full page reloads. Gmail and Figma are SPAs. They feel fast and fluid because navigation happens client-side, but they can be harder to optimize for SEO since search engines need the JavaScript to run before they see the content.

You know the feeling even if you do not know the term. In Gmail, clicking an email opens it instantly — no white flash, no page reload, no spinner in the browser tab. That is a SPA at work: the application loaded once, and everything after that is the app rearranging itself, the way a desktop program would. Old-style websites reload the entire page for every click.

Why it matters for your project: the SPA question is really a question about what you are building. If it is a tool people work inside — a dashboard, a booking manager, an internal admin panel — SPA-style interactivity is exactly right, and nobody Googles their way into an admin panel anyway. If it is a marketing site that lives or dies on search traffic, a pure SPA is the wrong default, because content hidden behind JavaScript is slower for search engines to index.

In practice this is rarely either/or. Frameworks like Next.js blend approaches: pages are rendered on the server (SSR) or pre-built (SSG) so search engines and first-time visitors get instant content, then the SPA experience takes over for interaction. The UI feels like an app; the crawlability stays like a website.