What is Longitude ?
Longitude is (noun) a position on the earth’s surface measured in degrees east or west of an imaginary line running north-south through Greenwich, a town just to the east of London. Antonym latitude COMMENT: Longitude and latitude are used to indicate the exact position of something on the earth’s surface. They are measured in degrees, minutes and seconds. London is latitude 51 degrees30’N, longitude 0 degrees5’W.
source: Easier English, Student Dictionary Upper Intermediate Level