This is an internal type used by the interpreter for processing expression evaluation results. It cannot be stored as an object property.
Conceptually at least, the storage of objects in variables works as if the variable assumed a Reference type.
A Reference item points at the property of an object. Therefore it consists of two parts: the base object and the property name.
It is ephemeral and is not necessarily implemented in the interpreter, but it is used in the ECMA standard to help explain how some of the internal algorithms operate.
It facilitates a simplified syntax grammar and therefore adds value in the understanding of how the internals of the grammar should behave.
It helps describe the operation of the delete and typeof operators, the assignment of values and function calls. It also assists in the grammar of the 'this' value for function calls that are associated with objects and used as methods.