Hosts file located under C:\Windows\System32\Drivers\Etc\hosts.
Host to name redirection meant to order the application that uses it to which IP address to regard.

Example: you have an Exchange server on your organization that located in DMZ at (Not published to Internet).

If the DMZ link is down for some reason and you want to route request to different IP as you put in HOSTS file (for all users use the exchange):

Mail_server_DNS_Name to

So syntax is: