NATO stands for North Atlantic Treaty Organization. It was formed in 1949 to provide collective security against the threat posed by the Soviet Union. The original members were Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States. Though the Soviet Union has long since fallen, now 29 nations are members of the alliance. To make it easier for so many countries to communicate, NATO has two official languages: English and French. This means that it also has two acronyms -- in French, NATO is OTAN, which stands for Organisation du Traité de l'Atlantique Nord.

Source: Defense.gov