In the context of MOSIP, identifiers are alphanumeric digital handles for identities in the system. While a person's identity is represented as a collection of biographic and biometric attributes that can uniquely identify the person, the identity is referred to using identifiers.
Unique Identification Number (UIN), as the name suggests, is a unique number assigned to a resident. UIN never changes and is non-revocable. UIN is randomized such that one should not be able to derive any Personal Identifiable Information (PII) from the number itself.
The VID / Virtual ID is an alias identifier that can be used for authentication transactions. The key characteristic of such an identifier is that it expires. This allows for free disclosure and usage of this identifier in various contexts. It is privacy friendly in a way such that it can be revoked, configured for one time usage and is not linkable. Since these are used for authentication transactions, such identifiers are to be known to the user only or generated with their participation.
The RID is the registration ID that is used to refer to the registration process. It is interchangeably used with the AID which represents the "Application Number" / registration ID that is used as the context for all communication with user for the registration.
The PRID is a specialized RID used in the pre-registration system.
The Token identifier is a system provided customer reference number for relying parties for identifying the user uniquely in their system. The token identifier is an alias meant for the relying party and us typically unique to them. This identifier is included in the response of the authentication transactions. One key differentiator is that the token identifier is not accepted as an identifier for authentication transactions.