This is a Profile that is setup under Lookup Values that could be an ID from another system which you can use to dedupe imports. Deduping on a Profile ID is beneficial when the contact/address information being imported is different to what is held in thankQ.
Scenario: Another database is used to capture updated information, for instance Schools. This information is exported with the parent/child id to an excel spreadsheet and imported into thankQ. If there are any changes in the address information the contacts can be deduped using the ID of the other database and updated in thankQ.