double-coincidence-of-wants
简单地说，这是指：生产A的人想要产品B，而生产B的人想要产品A。这是为了说明货币存在的必要性和重要性，因为同时存在这种情境的情况实在太少了。
原文：
The phrase double coincidence of wants was used in Jevons (1893). "[T]he first difficulty in barter is to find two persons whose disposable possessions mutually suit each other's wants. There may be many people wanting, and many possessing those things wanted; but to allow of an act of barter there must be a double coincidence, which will rarely happen." That is, paraphrasing Ostroy and Starr, 1990, p 26, the double coincidence is the situation where the supplier of good A wants good B and the supplier of good B wants good A.
The point is that the institution of money gives us a more flexible approach to trade than barter, which has the double coincidence of wants problem. Also known as dual coincidence of wants.