C
Cash application is the accounts receivable (AR) process of matching each customer payment to the invoices it pays and posting the payment in the ledger, so open balances and ageing show what customers still owe.
D
Days sales outstanding (DSO) is the average number of days a business takes to collect payment after making a sale on credit.
Dunning is the process of reminding business customers to pay overdue invoices, with each message getting firmer until the invoice is paid, disputed or escalated.
R
A remittance advice is a document or message a customer sends to a supplier to show which invoices a payment covers, how much is paid against each invoice and why any amount differs from the invoice total.