.htaccess tips and tricks

"What are .htaccess files anyway?
Simply put, they are invisible plain text files where one can store server directives. Server directives are anything you might put in an Apache config file (httpd.conf) or even a php.ini**, but unlike those "master" directive files, these .htaccess directives apply only to the folder in which the .htaccess file resides, and all the folders inside. "

http://corz.org/serv/tricks/htaccess.php