relating to a public body or its authority/authorization, actions, functions, or responsibilities;
e.g. He needs to obtain some official documents.
(adjective)
employed by a public body and thus holding a position of some trust and authority;
e.g. She is an official advisor to the president.
(noun)
a person who is employed in some public office or who has similar duties, especially representing an entity such as an organization or a government department;
e.g. He works as an official in the town's public health office.