A great circle is the largest possible circle that can be drawn on the surface of a sphere, such as the Earth. It divides the sphere into two equal halves and represents the shortest path between two points on the globe. Examples of great circles include the equator and the lines of longitude. When navigating or flying long distances, pilots and sailors often use great circles to determine the most efficient route. This is because traveling along a great circle minimizes the distance traveled, making it an essential concept in fields like geography, aviation, and maritime navigation.