The term for the imaginary line that divides the Earth into the Eastern and Western Hemispheres is the Prime Meridian. This line runs from the North Pole to the South Pole and is positioned at 0 degrees longitude. It serves as a reference point for global navigation and geography. The Prime Meridian is significant in defining time zones, particularly the Greenwich Mean Time (GMT). Its establishment has helped in standardizing time and coordinates across the world, facilitating international trade and communication.