The horizon is the line where the earth's surface and the sky appear to meet. It is the farthest point you can see when looking out over land or water. The horizon changes based on your elevation; for example, standing on a hill allows you to see further than when you are at sea level. In addition to its visual aspect, the horizon plays a role in navigation and geography. Sailors and pilots use the horizon as a reference point for orientation. The term "horizon" can also refer to the geographical horizon, which is the distance to the visible edge of the earth from a specific height.