refund 和 chargeback都有退款的意思，要是你用google搜索着两个词的定义，一大堆云山雾罩的（define:refund, define: chargeback）。
我查了BLACK法律词典还有网络的一些解释，尝试着整理如下：
1. refund 有退款的意思，按照BLACK法律词典是指多付款了的情况，要求对方付款（the return of money to a person who overpaid……），但如果你要查Longman, Collins等词典会告诉，买方对产品不满意，要求退货还款，也是可以用refund的。
2. chargeback, 在BLACK里的意思写的很清楚：A ban’s deducting of sums it had provisionally credited to a customer’s account, occuring usually when a check deposited in the account has been dishonored。 信用卡交易里面这个词会经常用到（A transaction returned through interchange by an issuer to an acquirer. A transaction may be returned because of it was non-compliant with the association rules and regulations or because it was disputed by a cardholder）。我看到一个比较令人信服的解释是，买家无法退货refund，就会主张chargeback（拒付）。
参考链接1，更 有价值的参考链接2 （美国的消费者，许多习惯先买了再决定要不要。 用了不喜欢就退货（refund），退货不成就拒付（charge-back）。美国的商家也了解会有消费者藉此图利，但以长期总的来看，藉由退货保证使消费者安心，可以促进用户即兴购买(”impulse buying” ) 的冲动性销费，让营业额增加。美国的商家也了解会有消费者藉此图利，但以长期总的来看，藉由退货保证使消费者安心，可以促进用户即兴购买(”impulse buying” ) 的冲动性销费，让营业额增加。拒付的人（用户）,只要提出信用卡公司接受的理由，信用卡公司会有纪录， 但不影响其信用。常见的理由- Charges not authorize; - Charges for undelivered goods or services; Charges for goods or services different from what was represented or of the wrong quantity; - Charges for goods that were not timely delivered.）
另外，还有2个与此相关的词，credit note 和 debit note。简单来说，credit note是你欠别人的，debit note 是别人欠你的。
wiki上对credit note的解释：A credit note is a monetary instrument issued by a seller that allows a buyer to purchase an item or service from that seller on a future date. Credit notes may be issued by a seller as a goodwill gesture to a buyer who wishes to return previously purchased merchandise (instead of cash repayment) in circumstances where the original sales agreement did not include an explicit refund policy for returned items. In such circumstances, a credit note of value equal to the price of the returned item is usually issued allowing the buyer to exchange his purchase for other items available with the sale.
A credit note is a monetary instrument issued by the business that allows a buyer to purchase goods or services from the business on a future date. It is used by the customer who wishes to return previously purchased merchandise and to purchase some goods or services on a future date.
A Credit Note or Credit Memo is a document used to adjust or rectify errors made in a sales invoice which has already been processed and sent to a customer. If you have already sent an invoice to a customer but now need to provide a credit for that invoice, you would send them a Credit Note or Credit Memo. You can think of a credit note as a “negative invoice.”
解释的好像很费劲，还是这个链接的解释比较好。
debit note:
欠款索要时出具的通知单（列明你要向客户／代理的应收款），例如：
若你是货代，帮客户承运了货物，你就可以开一个ＤＮ给他, 他回签确认, 即他默认了这笔款；
若你是出货方，帮客户代付了运费后要向客户出具ＤＮ，以收回代付款；
若你是买方，货款已付但短了货量，你可向卖方出具ＤＮ以求索回多付款项（若货代多付船东运费，同理．．．）
credit note：
贷记（或应付款）通知单（你应该向客户或代理付的款项），就如上debit note例子作反向理解即可：
若你是卖方，如果你的产品出了质量问题需要赔偿客户，或者上个定单客户多付了钱，或者客户帮你做认证垫付了一笔钱，这些属于你们应该赔付给客户的金额，都可以开具credit note来销帐。
大多时候这两种帐单只是用于调账（免去改动发票等相关单证的麻烦），即没有真正据此来收款付款，而在新定单中销帐．如在新定单的发票里面加上一项credit note／debit not，从而把相关金额减去/加上。
some examples of when you would use a Credit Note in TRADING
- Unit price overcharged or over-billed : For example you issued an invoice for an item for $1100 when the correct price of the item should have been $1010 instead. Therefore you need to issue Credit Note to give a credit of $90 to your customer for the amount over-billed.
- Goods short shipped : You invoiced a customer for 10 units of your product but only shipped 9 units to them by mistake. The customer then calls you to say that 9 units are okay and does not want the shortfall item at the moment. Therefore you need to issue a Credit Note to credit your customer for the shortfall quantity of 1 unit.
- Faulty goods returned or goods rejected by customer. You would issue a credit note for the goods returned to correct your Accounts Receivable and Inventory.
- Product Wrongly Shipped : You wrongly invoiced and shipped Product A when the customer actually ordered Product B which may or may not be at a different price. To rectify this, you would then ship Product B together with a Credit Note for Product A and another invoice for product B. This will restore the inventory and Accounts Receivable in your books while billing the customer for the correct item and amount. Meanwhile the customer returns the incorrect Product A.
- Discounts given after the invoice is issued : You sent an invoice for $1100. The customer then calls you asking for a discount and ask you to waive the $100 making the net invoice amount $1000. You agree to this in good faith. You would then issue a credit note for $100 to this customer to adjust for the discount given.
- To Write-off Customer Short Payment
- You send an invoice for say $2010. The customer sends you a short payment of $2000 only. You do not wish to recover the shortfall amount but your books indicate that $10 is still owing on this invoice. You can then issue a credit note of $10 to write-off the shortfall amount.