A meridian is an imaginary line that runs from the North Pole to the South Pole, helping to define geographic coordinates on Earth. Each meridian is measured in degrees of longitude, with the Prime Meridian at 0 degrees serving as the starting point. Meridians are essential for navigation and mapping, as they help determine the east-west position of a location. Meridians are often used in conjunction with parallels, which are lines of latitude that run parallel to the equator. Together, meridians and parallels create a grid system that allows for precise location identification on the Earth's surface. This system is crucial for various fields, including cartography, geography, and navigation.