The Pay Per Use feature captures license usage in a pay-per-use database which can then be sent to the vendor upon request. The database is authenticated, and its contents can be validated by the vendor.
For example, if you have an unrestricted use license that is paid for based on monthly usage, your vendor can request that you write the usage information to a pay-per-use database each month, and send the database file to them for billing purposes.
For information on configuring Pay Per Use, see License Server Configuration file and Enabling and configuring license server logging.
Usage databases use SQLite, a free open source database. You can find out more about SQLite at http://www.sqlite.org.