Here's a breakdown:

* Longitude: Lines of longitude run from the North Pole to the South Pole, measuring how far east or west a location is from the prime meridian.

* Prime Meridian: This is the zero-degree line of longitude, passing through Greenwich, England. It's the starting point for measuring longitude.

Important Note: Longitude is measured in degrees, ranging from 0° at the prime meridian to 180° east or west.