An invoice is a document that is sent by a supplier, vendor or service provider to a customer, indicating the goods or services provided and the amount due for payment. It typically includes details such as the date of the invoice, the customer's name and address, a description of the goods or services provided, the unit price, the total amount due, and the terms of payment. It may also include any applicable taxes or discounts. An invoice serves as a request for payment and is often used as a record of transaction.

Invoicing is a critical step in the accounting process and is an important tool for managing cash flow in a business. Invoices are also used as a basis for recording income and expenses, and for tracking the status of payments from customers. Invoicing can be done manually or electronically, and there are different software available that can help with the process, such as invoice management software, billing software and accounting software.