Parallel circles are imaginary lines that run around the Earth, maintaining a constant distance from the equator. These circles are also known as lines of latitude, with the equator itself being the most significant one at 0 degrees latitude. As you move north or south from the equator, the latitude values increase, reaching 90 degrees at the poles. These circles help in navigation and mapping by providing a reference system for locating positions on the Earth's surface. Each parallel circle is measured in degrees, and they are essential for understanding global geography, climate zones, and time zones, such as the Prime Meridian and International Date Line.