A redirect allows you to send both users and search engines from one URL to a different URL. There are a number of different redirects; the most popular being 301 and 302.

A 301 tells search engines that a redirect is permanent and that the SEO juice from the old domain should be passed on to the redirected page. Typically between 90-99% of the ranking power is passed on.  

A 302 redirect indicates to search engines that the redirect temporary.

A permanent 301 redirect is commonly used when a new domain name has been purchased and a user wants to redirect the traffic from the old site to the new web address. 

A common use for a  302 redirect is when you have a site with a page still under construction, but you want to let the public know that it’s being worked on and will be live soon, so you could redirect to a placeholder page with information of what’s being worked on.