301 redirect
A 301 redirect is a permanent instruction that a URL has moved, passing visitors and accumulated ranking signals to the new address.
In full
A 301 redirect is an HTTP status code meaning the requested resource has moved permanently. Browsers follow it to the new location and search engines transfer the ranking signals the old URL had accumulated. A 302 redirect, by contrast, signals a temporary move and does not reliably pass those signals, which makes choosing between them consequential rather than cosmetic. Redirects should point to the closest genuine equivalent page. Redirecting many URLs to a homepage is technically a redirect and practically a deletion, since search engines commonly treat an irrelevant destination as a soft 404.
Why it matters
Missing 301 redirects are the single most common cause of a website redesign losing organic traffic. Every URL that changes needs one, mapped before launch rather than diagnosed afterwards.