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Sending parts of a page to the browser as soon as they're ready instead of waiting for everything — like serving each dish as it's cooked instead of waiting for the whole meal.
A rendering technique where the server sends HTML in chunks using Suspense boundaries. The browser can display available content immediately while waiting for slower parts (data fetches, heavy computations) to resolve and stream in.
Streaming SSR leverages React's renderToPipeableStream (Node) or renderToReadableStream (Edge) to emit HTML progressively. Suspense boundaries delineate streaming segments: the shell renders immediately with fallback UI, and resolved segments are injected via inline <script> tags that swap the fallback. This reduces Time to First Byte and First Contentful Paint. Next.js implements this via loading.tsx files, which compile to Suspense boundaries around page components.