In this directory is where the web site files will be placed. The index page located in this directory is what will load when a visitor visits your website.
This directory can be used for storage of files that should not be web accessible, such as .htpasswd files or configuration files.
If the web site has raw logs or web site statistics enabled this is where the web server logs will be placed.
If web site statistics are enabled this is where the generated web pages for the statistics will be placed.