NATO stands for the North Atlantic Treaty Organization. It is a military alliance established in 1949, initially formed to counter the threat of Soviet expansion during the Cold War. The organization is based on the principle of collective defense, meaning that an attack against one member is considered an attack against all members. NATO's membership includes countries from North America and Europe, and it serves multiple purposes, including crisis management, cooperative security, and promoting democratic values. Over the years, NATO has adapted to address various global security challenges, including terrorism and cyber threats.