301 is one of many status codes that a server sends to your web browser.
Other possible codes include 404 – Not Found, 403 – Forbidden, and 500 – Server Error. If you visit a website and it sends the page normally, the status code that attaches to the page is 200 – OK.
When you change your address, do you ask the Post Office to forward your mail to your new place? A 301 Redirect can be thought of in the same way. Anyone who attempts to visit a URL that you have changed or removed will get a 404 message if you don’t put 301 redirect in place.
See this list of all HTTP status codes for more information.