Definition: DNS0 refers to the term "Distributed Not-Reachable Services". In the context of internet services, it could refer to a situation where an application or network service does not have a direct connection to the server on which it operates (also known as a 'reachable' system). This is often used in scenarios where a client needs to connect to a remote server without needing to directly contact that specific server, such as when using a public WiFi hotspot.