Extended definition
Way of redirecting one page to another. 301 = permanent (transfers most SEO authority). 302 = temporary (doesn't transfer authority).
Context and application
Redirect chains (A → B → C → D) are SEO killers — each hop loses a bit of authority and slows down crawl. Periodically check chains with an audit. Redirect loop (A → B → A) completely blocks indexing. 302 used incorrectly (instead of 301) is one of the most common mistakes on site migrations — Google doesn’t transfer authority and new pages start from scratch. If you’re A/B testing on a new URL, OK use 302. If the old URL is permanently removed, always 301.
In practice
when you change URL structure on the site, you use 301 for old pages → new ones.
Related terms
Canonical URL, Indexing.