A gateway is a merchant service provider that facilitates transfers of funds between customers and businesses. Within the context of Fusebill, this is a third party that processes your credit cards. Fusebill will make requests to your gateway in order to request a transfer of funds, from a customer's credit card to your gateway account. The gateway later releases funds to the bank account you have linked to your gateway account. In many cases, they will also deduct their transaction fees during this deposit.
When attempting to reconcile between the deposits to your bank account and the cash ledger information in Fusebill, the Gateway holds the balance and the financial transactions that have taken place.
Information on how to configure a gateway(s) can be found here Configuring Gateways