形式发票（Proforma Invoice）是一份写有所销售货物名称、规格、单价等信息的非正式的参考性发票。简称PI。

它是应进口商的要求，由出口商开出的。顾名思义，形式发票不是正式发票，没有任何约束力。而商业发票则是出口商开给进口商的用经收货记账并支付货款和报关的正式发票。

A number of Latin terms are used in legal terminology and legal maxims. This is a partial list of these "legal Latin" terms, which are wholly or substantially drawn from Latin.

In contract law, and in particular the requirement for consideration, if no fixed price is agreed upon for the service and/or materials, then one party would request a reasonable price for the said services and/or materials at the end of the job. A common example would be a plumber requested to fix a leak in the middle of the night.