Dateline (Newspapers, magazines, web pages): The location, date, and sometimes the source of the story. Example: New York, Sept. 27 (AP)
(Radio) "New York:" or "In New York today,"
(Television) The story's location fonted on-screen, e.g. "The White House," or recited by the newsreader.
The dateline tradition began in the early days of newspaper reporting, before telegraph or telephone communications, when there was a time lapse of hours or days between the reporter's transmitting the story and its being printed in the paper.
It is the name source for Dateline and two other shows of that name.
Variant: An episodic news program (e.g. CBS Evening News, The Daily Show) will often display today's date at the front of the program for the benefit of anyone who needs to later identify the episode.