Bastion
A bastion is traditionally considered to be a host/server/service which is exposed to the Internet and as such required particular attention be made to its security and isolation through firewalling when communicating to public and private networks. In the interconnected world of web hosting pretty much every service is considered publicly accessible and requires the upmost attention to security.
Pipe Ten typically makes an onion based approach to security; where every host has a local firewall, every network has its own firewall, every role has its own network, everything is monitored, alerted and subject to ongoing audit.