Final answer:
The piece of paper that proves you have bought an item is called a receipt. It serves as evidence of a transaction and includes details such as the seller's name, purchase date, item description, and price.
Step-by-step explanation:
The piece of paper that proves you have bought an item is commonly referred to as a receipt. It serves as evidence of a transaction between a buyer and a seller. A receipt typically includes details such as the name of the seller, the date and time of the purchase, the description and price of the item, and any applicable taxes or discounts.
For example, when you buy a book from a bookstore, they will give you a receipt as proof of your purchase.
Having a receipt is important as it can be used for various purposes, such as returning or exchanging items, keeping track of expenses, or claiming warranties.