The mid-ocean ridge system (MOR) is a system of mountains that run through all four of the ocean basins. In order to understand just what they are, you need to understand a little about plate tectonics. To put it simply, Earth's outermost layer is mostly rigid and is broken up into sections that we call plates. These plates are in constant motion (moving at a rate of a few cm/year). As they move, they interact with each other along the boundaries between plates. At some boundaries, the plates are coming togethe, At others, they are pulling apart. At still others, they are just sliding past each other. The MOR's mark the places where two plates are pulling apart and they wind around Earth's surface for over 43,000 miles. If you go to http://www.ngdc.noaa.gov/mgg/image/2minrelief.html, you can see a series of maps that show the ocean floors. On these maps, you can trace the MOR as it comes out of the arctic and across Iceland. From there it goes down the center of the Atlantic, around the southern tip of Africa, and into the Indian ocean. In the Indian Ocean. the ridges split. One branch goes northward and eventually disappears into the Red Sea. The other goes around the south of Australia and up into the East Pacific Ocean where it eventually disappears into the Gulf of California. Note, this is a very short answer covering a topic that usually takes me 2 or 3 hours to cover in lecture. So, I am really only able to just scratch the surface in this forum.