A ".htaccess" is a file that can change settings on the servers and allow you to do many different things such as alter .shtml extensions and create custom 404 and 505 error pages. .htaccess files are used most on Unix or Linux servers, or any version of the Apache web server. You do however have to have permission from your host to use a .htaccess file. Along with the above things a .htaccess file can also password protect folders and redirect users automatically. When using a .htaccess file for changing your file extensions such as ssi this can slow down the speed of your web pages.