React
Hydration
Attaching React to server-rendered HTML, reusing the markup rather than recreating it.
Why interviewers ask about it
Mismatches come from non-determinism in render: Date.now(), Math.random(), localStorage. Move those into useEffect so the first client render matches the server.
Related terms
This term is part of the free Python Full-Stack interview preparation module - browse the full glossary for every definition.