Recurring billing is the merchant's side of recurring payments: the practice of charging a customer automatically at agreed intervals, such as monthly or yearly, using payment details the customer has authorized the merchant to keep. The main entry explains how these payments are authorized and processed. Recurring billing as a term puts the emphasis on the seller's process of creating charges, rather than on the movement of funds.
In card acquiring, a recurring charge is submitted by the merchant without the cardholder present, as a merchant-initiated transaction that refers back to the first payment in the series. Card network rules require the merchant to obtain clear consent to the terms, flag the transactions correctly and offer a simple way to cancel. Bank-based equivalents use a direct debit mandate.
Billing systems add the commercial logic around the charge. They hold the price plan and billing cycle, raise invoices, apply proration when a plan changes and run dunning when a payment fails. Where the product is an ongoing service with plans and renewals, the wider discipline is usually called subscription billing.