What is a geographic grid? How does the geographic grid serve the same purpose as co-ordinates on a graph?

A framework of lines of longitude and latitude on a globe or a map is called a geographic grid.

This grid on the globe or the map serves the same purpose as the system of coordinates on the x-axis and y-axis on a graph paper. In this case the x-axis is represented by lines of latitude (horizontal) and y-axis, by lines of longitude (vertical). These lines help to locate places on the earth.