It seems you're thinking about the lines that divide the Earth into hemispheres. Here's the breakdown:

* The Equator: This is the most well-known line, dividing the Earth into the Northern Hemisphere and the Southern Hemisphere.

* The Prime Meridian: This line runs from the North Pole to the South Pole through Greenwich, England. It divides the Earth into the Eastern Hemisphere and the Western Hemisphere.

Let me know if you had something else in mind!