Weapon of mass destruction
Appearance
A weapon of mass destruction (WMD) is generally taken to be a type of weapon which is designed to kill large numbers of people, usually civilians but also potentially military personnel. Weapons of mass destruction are generally considered to be of limited military usefulness because their destructiveness is likely to trigger an extreme response.
The types of weapons traditionally considered to be of this variety are:
Countries that may possess WMD
According to the Federation of American Scientists, over 30 countries may possess WMD. Their assessment is at http://www.fas.org/irp/threat/wmd_state.htm