In 1947, the United Nations General Assembly declared 24 October, the anniversary of the Charter of the United Nations, as which “shall be devoted to making known to the peoples of the world the aims and achievements of the United Nations and to gaining their support for” its work.
In 1971 the United Nations General Assembly adopted a further resolution (United Nations Resolution 2782) declaring that United Nations Day shall be an international holiday and recommended that it should be observed as a public holiday by all United Nations member states.
United Nations Day is devoted to making known to peoples of the world the aims and achievements of the United Nations Organization. United Nations Day is part of United Nations Week, which runs from 20 to 26 October. [WIKIPEDIA]