What is an international non-governmental organization (INGO)?

The United Nations Economic and Social Council (ECOSOC) defines an INGO as "any organization which is not established by inter-governmental agreement" (Resolution 288 (X) 27 February 1950), "including organizations which accept members designated by government authorities, provided that such membership does not interfere with the free expression of views of the organizations" (Resolution 1296 (XLV) of 25 June 1968).