A Credit Advance is defined as a credit posted to a Guardians account that does not currently have outstanding debits to offset it. In this case SchoolLeader will identify this situation at bookclose and mark the balance as a Credit Advance.
This is typically done when you want to "advance" a customer a credit before the service has actually been rendered such as when you give someone a $100 credit for future charges.
Since the A/R subaccounts can never have a credit balance (its impossible to sell negative products or services) these credits are held in a special Subledger account called CREDITADV-Credit Advances.
When services (debits) are posted to the subledger these credit advances are moved into the accounts to offset the charges.