Index Token
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A random value, drawn from a table of random values, that stands in for a particular PAN. Nothing about the token can be computed from the PAN or the PAN from the token; only the table, held by the tokenisation system, connects them.
Applies to. Entities that render stored PAN unreadable by tokenisation. 3.5.1 names index tokens as one of its four accepted methods.
Example. A customer's card is stored as the value 7f3a-91c2-... in the order system, and the mapping to the real PAN lives in a separate vault. The order system is out of the business of holding PAN; the vault is entirely in it.
Limits. An index token is only as strong as the table's protection, so the vault, its keys and everything that can reach it are in scope, and 3.5.1's guidance treats the tokenisation system as part of the CDE. A token derived from the PAN by a formula, or reversible without the table, is not an index token and does not meet the control. The card networks' payment tokens are a different mechanism with the same name.
In PCI DSS v4.0.1. 3.5.1