Final answer:
The lines measured from the prime meridian towards the east and west are known as meridians or lines of longitude, used to determine a location's east-west position on Earth.
Step-by-step explanation:
The lines on the Earth measured off the prime meridian towards the east and west are called meridians or lines of longitude. The prime meridian is the reference line for longitude and is set at 0 degrees longitude, running through the Royal Observatory in Greenwich, England. Longitude specifies the east-west location of a place and is measured in degrees east or west of the prime meridian. On a global scale, longitude lines run from the North Pole to the South Pole and are used in coordination with latitude lines to pinpoint locations on Earth. The prime meridian is an imaginary line that runs through the Royal Observatory in Greenwich, England, and is defined as 0 degrees longitude. All meridians east of the prime meridian are numbered from 1 to 180 degrees east (E), while those west of the prime meridian are numbered from 1 to 180 degrees west (W).