system identifier
Technical computing term for a unique name or code that identifies a system, often used in markup, databases, or configuration.
In an XML declaration, a system identifier is sometimes used to specify the location of the DTD.
Compound of システム (system) + 識別子 (identifier). 識別子 itself is a modern technical coinage from 識別 (identification) + 子 (a suffix for small or concrete things, here used in the sense of a token or label).