The Four Corner Model is the basic model for understanding payment processing. The essence of payments processing is a Payer wanting to transfer funds from its account at his bank to the account of the Payee held at the same or another bank.
The basic process is that the Payer instructs his bank in some shape or form to take funds out his is bank account an put it in the account of the Payee. The Debtor Bank than transfers the funds to the Creditor bank after which the Creditor Bank credits the account of the Payee.
This model is the basic form used to explain payment processes, for different payment processes additional players can appear.
Terminology
The payment industry uses a lot of terms to identify the same object or sometimes uses the same terms but with a slightly different meaning. The terminology used can be specific for a certain domain.
For example, in Card processing the Payer is often referred to as “Cardholder” or “Consumer” where in ACH payments the Payer is often referred to as “Debtor”. Similar in Card Payments the Payee is mostly referred to as “Merchant” and the Creditor Bank as “Acquiring Bank”.