Trying to Understand the Meaning of an Invoice? Here’s What You Need to Know. The term “invoice” can be confusing at first, as it is frequently used, but not always fully understood. Essentially, an invoice is a document that signifies a transaction between a buyer and a seller for goods or services that have been sold. For the seller, an invoice serves as proof of the sale and is crucial for receiving payment. For the buyer, an invoice is a bill for the items or services purchased. While they may seem daunting, invoices are a necessary part of doing business, and accuracy is vital. And who knows, they might even be enjoyable, especially when you get paid promptly!