The parallel of latitude 66° 33ʹ south of the equator. It marks the southernmost point at which the sun is visible on the southern winter solstice and the northernmost point at which the midnight sun can be seen on the southern summer solstice.
Definition of Antarctic Circle in US English:
Antarctic Circle
proper noun
The parallel of latitude 66° 33ʹ south of the equator. It marks the southernmost point at which the sun is visible on the southern winter solstice and the northernmost point at which the midnight sun can be seen on the southern summer solstice.