Overview#Identifier (ID) (UserIds and Unique Identifiers Identity Attributes) is an Attribute that unique provides Identification of either a unique "Entity" or class may be an idea, physical Entity (or class thereof), or physical substance (or class thereof) within a provided Context
An Identifier may be a Name Form, word, number, letter, symbol, or any combination of those.UserIds and Unique Identifiers as we use them are Identifier RFC 6973 Section 3.3 defines Identifier as A data object uniquely referring to a specific identity of a protocol entity or individual in some context. See RFC 4949.
Identifiers can be based upon any Name Form Official Names, Personal Names, and/or nicknames or can be artificial (for example, x9z32vb). However, identifiers are by definition unique within their context of use, while natural names are often NOT a unique Identifier.