Universal Standard Dollar
The Universal Standard Dollar is a vaguely defined currency rarely used directly but often used to compare currencies especially in documents and discussions not specific to any one nation or group of nations. For many, its only use is as such a meaningless abstraction as no real government stands behind any such currency. Its value is imaginary and essentially exists to provide a medium of exchange between nations who cannot agree on which currency to use or in contexts designed to be as non-specific as possible.
Sometimes, but not always, it's value is considered roughly equal to the real life USD, the U.S. Dollar. Less common comparisons are the Euro, the British Pound, and the Australian or Canadian dollar. Often times when one player gives a price in USD meaning U.S. Dollar, another player may interpret it as a Universal Standard Dollar to avoid confusion or conflict.