Status code (Redirect, HTTP status code, HTTP response status code, Browser error code)

A server response when the browser requests a webpage.

There are five types:

1xx – informational responses
2xx – success (200 – the request succeeded)
3xx – redirection (301 – moved permanently, 302 – temporarily moved, 304 – not modified, 307 – temporary redirect, 308 – permanent redirect)
4xx – client error (403 – forbidden, 404 – not found, 410 – gone, 429 – too many requests)
5xx – server error (500 – internal server error, 501 – not implemented, 503 – service unavailable, 550 – permission denied)
Crawlers use these to determine the health of a website and discovering and fixing some of these will have an impact on your rank.