Meridian through the Royal Observatory, Greenwich, England; the standard reference for longitude and Greenwich time.
the line of 0o longitude which passes through Greenwich, England; also known as first or prime meridian
the meridian designated as 0 degrees that runs through Greenwich, England, and serves as the base line for measurements of longitude.
This is an imaginary line of longitude - it's also the 0 degree meridian. It is used as a reference to measure longitude east and west. It passes through Greenwich, England. It's also called the prime or international meridian.
The central meridian line from which all time zones are set.