What are the meridians and how does the Greenwich Meridian divide the planet Earth?

A meridian is the half of the imaginary great circle on the Earth's surface terminated by the North pole and the South pole, connecting points of equal longitude

Explanation:

The imaginary prime meridian divides the globe into Eastern and Western hemispheres. The meridian divides the globe just as the equator divides the globe into Northern and Southern hemispheres. The meridian is 0° longitudes same as the equator is 0° latitude.