.htacess is a filed used by Apache Web server software to effect various configurations to the directory where it is located. It is a hidden file in unix based systems (since its name starts with a dot), and is placed in the root of the directory in which it is supposed to alter the configurations of the web server to allow or limit services. It is basically a file that contains coded information that guides the server on how to execute various functions.

The importance of .htaccess file

It can regulate the permissions that are used to access certain areas. This can include blocking access to unregistered people, to certain users, or even to some IPs and web crawlers.
Also, it can be used to give redirection instructions when there are various URLs to the same page. This is helpful for search engine optimisation.
Also, .htaccess can be used to redirect to error messages whenever the requested file cannot be found.