An Identifier is a designation to indicate whether an academic appointment track is primary, dual, joint, administrative, etc.
The Primary identifier is the home department. Other academic appointment identifiers include Dual (additional appointments within the same school [e.g., appointments in Biology and Chemistry in Arts and Sciences]), and Joint (additional appointments across schools [e.g., Economics in Arts and Sciences and International Business School]).
Administrative appointments, such as, department/program chairs or deans, are indicated by the Administrative track type and identifier.