Definition - What does Meridian mean?
A Meridian is an imaginary line passing through the North to the South Pole of the Earth's surface. It is usually known as line of longitude. Longitudes and latitudes play an important role in locating any point on Earth. Since each Meridian is of same length equivalent to the Earth's circumference, the Meridian divides the Earth into 2 equal parts, also known as hemispheres.
Petropedia explains Meridian
The Meridian longitude, also known as line of longitude is a line across the Earth's surface that runs from the North to South Pole. Geographically, longitudes and latitudes are crucial points which help in locating a place on the Earth. Meridian lines or lines of longitude are set by the angles, which are defined based on the intersection of each Meridian with Prime Meridian. The Prime Meridian is a line of longitude located in Greenwich, England which is set at 0°. Meridian lines are perpendicular to the latitude lines of the Earth.