The definition published at ngo.org is:
A non-governmental organization (NGO) is any non-profit, voluntary citizens' group which is organized on a local, national or international level. Task-oriented and driven by people with a common interest, NGOs perform a variety of service and humanitarian functions, bring citizen concerns to Governments, advocate and monitor policies and encourage political particpation through provision of information. Some are organized around specific issues, such as human rights, environment or health. They provide analysis and expertise, serve as early warning mechanisms and help monitor and implement international agreements. Their relationship with offices and agencies of the United Nations system differs depending on their goals, their venue and the mandate of a particular institution.
See also http://www.ngo.org
It is interesting to note that ngo.org fails to mention the significant difference between a NGO and a NPO.
According to "Difference between" a NGO is:
Non-governmental organizations are created by legal persons who are not part of the government. Although NGO funds are mostly raised by the government, they maintain a non-governmental position, and eliminate the need for a government council. This type of organization is also known as a civil society organization. There are forty thousand international NGOs in the world, with the most organizations found in India.
In 1945, after the establishment of the United Nations Organization, the non-governmental organizations became extremely popular. Although, before this time, there were other organizations, such as the famous Rotary International, that began its operation in 1904. By the end of the year 1914, there were one thousand and eighty three NGOs in existence. International NGOs played a vital role in the anti-slavery movement, as well as in the movement for women’s suffrage. The official definition of international NGOs was defined on February 27, 1950, by the resolution 288 (X) of the ECOSOC.
A NPO is a private non-profit organization that uses its extra funds for the purpose of the organization, rather than dividing it between the shareholders. Examples of NPOs are public arts organizations, charitable organizations and foundations.
The Ellenbach Foundation is a NPO.See also : difference between NPO and NGO