USD explained: A guide to the US dollar Ben Lobel May 25, 2021 11:42 AM The US dollar is the world’s reserve currency and the currency of the world’s largest economy, making it a powerhouse in the forex market. Discover everything you should know about USD before you open a position. Share: Introduction to the US dollar The US dollar is the national currency and legal tender of the United States, the largest economy in the world. It is also regarded as the world’s reserve currency, meaning it is held in large quantities by international central banks. Additionally, USD is used as official currency by a range of other sovereign nations worldwide, for example Ecuador and Zimbabwe.