Meridian

Meridian (astronomy): an imaginary circle perpendicular to the horizon.
Meridian (Chinese medicine): an important concept in traditional Chinese medicine.
Meridian (geography): either half or a full great circle that connects the Earth's poles. Also 0 longitude.
Meridian (perimetry, visual field): a polar coordinate system for the visual field.
The name of some places in the United States of America:

Meridian is also a novel by Alice Walker.
Meridian Broadcasting has been the ITV station for the south of England since 1992.
Meridian Energy Limited is a New Zealand electricity generation and electricity retailing company.
Meridian was a comic book series published by CrossGen in the early 2000s, and was the name of a city-state in that comic.
Meridian is the name of a line of business telecommunication products produced and marketed by Nortel Networks.

Meridian is also a term used by the Public Land Survey System in the United States.
Meridian is the Capital of Nosgoth in the Legacy of Kain series of video games.
DJ Meridian is a drum and bass musician in New York.
Meridian 59, an online game.
The British Rail Class 222 trains are known as Meridians and the services they are used on are named Midland Mainline Meridian services.
Meridian (DS9 episode) is a third season episode of Star Trek: Deep Space Nine.
Meridian is the name of an Australian Gothic Rock band.