A merchant agrees to give their customer a one-time discount for one of their products...

According to the Adobe Commerce Merchant Documentation, you can apply a custom price for a product when creating an order from the Admin Panel by selecting Custom Price checkbox on its line item row and entering a new price in dollars.

References: https://docs.magento.com/user-guide/sales/order-create.html#apply-a-custom-price-to-a-product