Server rendering
Producing a page's HTML before it reaches the browser — at build time, per request, or on a schedule — instead of leaving the browser to assemble it.
The three timings answer one question differently: how fresh must this be. Built once at deploy is fastest and staleest; rendered per request is always current and costs a server round trip; revalidated on a schedule serves the cached copy and refreshes it behind the reader's back.
The choice is per page, not per site. A news index that changes hourly and an about page that changes yearly have no reason to share a strategy, and the mistake that costs most is rendering everything per request because one part of the site needed it.
What all three buy is a first paint that does not wait for JavaScript, and markup that exists for readers who never run any — search crawlers, agents, feed readers, and anyone whose script failed to load.