What is the meaning of 301 redirect

A 301 redirect is a permanent redirect from one URL to another. 301 redirects send site visitors and search engines to a different URL than the one they originally typed into their browser or selected from a search engine results page. 
The 301 status code means that a page has permanently moved to a new location. 301 redirects are particularly useful in the following circumstances: You’ve moved your site to a new domain, and you want to make the transition as seamless as possible. If you have an equivalent piece of content that matches the page you’re replacing well, then a 301 redirect is usually your best option.