Nuclear-weapon States outside the Treaty on the Non-Proliferation of Nuclear Weapons refer to countries that possess nuclear weapons outside the Treaty. Among them, India, Pakistan and North Korea are illegal nuclear-armed countries; Israel, Iran and Japan are nuclear hiding countries. The United States, China, Russia, France and Britain are recognized as nuclear-armed countries.

A nuclear-armed country refers to a country that openly admits to possessing nuclear weapons and is recognized by the international community as legally possessing nuclear weapons. A country recognized as a nuclear power can use nuclear weapons to attack other countries in war without violating international law. According to the Treaty on the Non-Proliferation of Nuclear Weapons, only the five permanent members of the UN Security Council are recognized as nuclear-armed countries.

Countries that openly test nuclear weapons violate the Treaty on the Non-Proliferation of Nuclear Weapons and are regarded as illegal nuclear-armed countries by the international community. Illegal nuclear-armed countries are not allowed to use nuclear weapons to attack other countries in war, and once used, they will face the investigation of relevant international laws.

A hidden nuclear country refers to a country suspected of secretly and illegally developing and possessing nuclear weapons, but not openly conducting nuclear tests and claiming to possess nuclear weapons.