An address is a string that unambiguously describes what it refers to.
An address is only meaningful in the context of a protocol, which specifies how the address should be interpreted. This is true not just of Unrival addresses, but of any addresses. For instance, an IP-address tells a router where a resource can be found, but since there is no guarantee that the data eventually found there is the data expected, it does not qualify as an Unrival address. Similarly, postal addresses only make sense given a system of interpretation.