In geography, longitude refers to the imaginary lines that bisect the globe through the North and South Poles (the ones that run vertically, as opposed to the lines of latitude that run horizontally, parallel to the equator).
2 main lines of longitude
Meridians (lines running from pole to pole) connect points with the same longitude. The prime meridian, which passes near the Royal Observatory, Greenwich, England, is defined as 0° longitude by convention. Positive longitudes are east of the prime meridian, and negative ones are west.
