Advances are available to support those in immediate financial need until their first Universal Credit payment is made.
If an advance of benefit entitlement is taken, this means that a claimant can receive 13 payments over the course of a year instead of 12. As of October 2021 the period over which you have to repay an advance also doubles from 12 months to 24 months
The department published a set of supplementary management information on the number of Universal Credit Advances paid by the four advance types. It is available at https://www.gov.uk/government/publications/universal-credit-declarations-claims-and-advances-management-information.