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A React component that runs on the server and sends only the finished HTML to the browser — like a chef who plates the dish in the kitchen instead of cooking at your table.
A component that executes exclusively on the server, can directly access databases and file systems, and sends a serialized UI payload (not raw HTML) to the client. Server Components reduce client bundle size because their code never ships to the browser.
RSC introduces a dual-graph model: server components produce a serialized React tree (the RSC payload/Flight format) that the client reconciler can merge with client component subtrees. Server components can be async, have no hooks or state, and their closure data is serialized via the RSC wire protocol. Module references ($$typeof: Symbol.for('react.module.reference')) enable lazy loading of client component bundles at the boundary.