A 301 redirect is the HTTP status code for "moved permanently" — telling browsers and search engines that the requested URL has permanently moved to a new location. Returned by the server with a Location header pointing to the destination URL.
301 redirects are the right tool for permanent URL changes: site migrations, URL structure refactors, consolidating duplicate pages, fixing canonical issues, retiring outdated content. Google passes roughly 90-100% of the source URL's link equity to the destination — a topic Google clarified explicitly in 2016 (previously rumored to be 85-90%).
302 redirects (temporary) work for genuinely temporary moves (A/B tests, temporary maintenance pages) but pass less link equity and signal Google that the URL might come back. Use 301 for anything permanent.
For SEO, redirect chains are a quality issue — URL-A 301s to URL-B 301s to URL-C dilutes link equity slightly with each hop. Aim for single-hop redirects directly to the final destination. For AEO, the same logic applies: AI crawlers follow redirects but penalize chains by sampling less frequently.