Firewall term explained
Same as the firewall is a special software for secure network connections. Has the ability to restrict incoming and/or outgoing traffic on a number of conditions. Regarding SEO and web sites, a firewall blocks unwanted connections from the outside, such as connections by robots or other spam bots, increasing the load on the server.
Schematic representation of the firewall
If for any implicit reasons search engines don't index the site, you may want to check the settings of the firewall or contact the server administrator.