In Plain Terms
Static Site Generation (SSG) builds every page to plain HTML ahead of time, at build/deploy time, and serves those files directly — fast, cheap to host, but the content is only as fresh as the last build. Server-Side Rendering (SSR) generates the HTML on-demand, per request, on a server — always current, at the cost of a server doing work on every visit instead of just serving a static file.
Why This Matters for SEO and GEO
Both approaches serve fully-formed HTML to crawlers and AI bots on first load, which is what makes them both strong choices over a client-side-only rendered app (where a crawler may see an empty shell before JavaScript runs). This site itself is fully static-generated for exactly that reason — verifiable by fetching it with a Googlebot user agent and seeing the same content a browser gets.
How to Actually Choose
Content that changes rarely per page (marketing sites, documentation, most service pages) fits SSG well — it's simpler to host and effectively free to scale. Content that's genuinely different per request (a logged-in dashboard, personalized results, live inventory) needs SSR or a hybrid approach. Most marketing sites default to SSG unless there's a specific reason not to.