It is used for password authentication to certain areas of your
web site.
DETAILED SOLUTION
Best explained by the following links.
LINKS TO OTHER RESOURCES
- good explanation of .htaccess and how to use it
http://hoohoo.ncsa.uiuc.edu/docs/tutorials/user.html
- information specific to the Apache web server (much can be ignored)
http://www.apacheweek.com/features/userauth