What is the ACC activity type in History tab of Bill Inquiry?

What are the ACC activities on the history tab of Bill Inquiry? 

• Munis
• Accounts Receivable
• Bill Inquiry
• Bill Activity

With the Accounts Receivable changes in V2019.1, the ACC activity type was introduced. This activity type is the accumulated interest on the bill at the time of the payment and is created prior to applying the payment.  If the ACC activity is larger than the payment applied, the bill will have held interest that will need to be paid by subsequent payments

When reversing a payment, Munis will automatically reverse an associated ACC activity from the bill.