Joomla! Documentation™

• Cookie Domain Overrides the site's default cookie domain with the domain added here. The most likely situation when this would be needed is when the Joomla site is “bridged“ with other sites (e.g. forum or e-commerce) in sub-domains of the Joomla site. The default cookie domain may be like www.example.com, but using .example.com (note the leading dot) here will deliver cookies valid for any sub-domain of example.com.
• Cookie Path Overrides the site's default path for which the cookie is valid with the path added here. This may be needed if you have several Joomla installations in sibling folders.