Latitude, on Earth or another planetary body, is the angular distance north and south of the equator, measured in degrees. The small circle (geometry) formed by the collection of points with the same latitude is often called a parallel. The latitude of the equator is 0 degrees, while north and south poles are 90 degrees north latitude and 90 degrees south latitude, respectively.
As all meridians are halves of great circles, on Earth, a degree of latitude is equal to about 111 kilometers (69 miles), just as a degree of longitude along the equator is. However, Earth is not a perfect sphere but is slightly flattened at the poles and bulges slightly at the equator. Because of this, there are small differences in the length of a degree latitude.