The US Dollar Index (USDX) is a measure of the value of the United States dollar in relation to a basket of foreign currencies.
Currently the basket of trade partner currencies consists of the euro, Japanese yen, British pound, Canadian dollar, Swedish krona and Swiss franc.
The basket of trade currencies is overdue for revision as South Korea, China, Mexico and Brazil are now major trading partners with the US.
The index started with a base of 100.000. If the current index value says 99.00, this means that the dollar has fallen 1% since the start of the index against the basket of currencies over a specific time period.
The USDX can be traded as a futures contract on the ICE exchange.