A 301 redirect is a permanent redirect which passes between 90-99% of link juice (ranking power) to the redirected page.

Whenever you change your links, make sure you include 301 redirects to pass on your SEO link juice.

It is a permanent redirect which passes between 90-99% of link juice (ranking power) to the redirected page. 301 refers to the HTTP status code for this type of redirect. In most instances, the 301 redirect is the best method for implementing redirects on a website.

301 is called as permanent redirection.
It helps to re-direct an old url to the a new one and also the traffic of the old url gets transferred to the new one.