Real Dictionary

Arctic Circle
proper noun: The Arctic Circle is an imaginary line drawn around the northern part of the world at approximately 66° North.

Arctic Circle in American English
an imaginary circle parallel to the equator, c. 66°34′ north of it
noun: an imaginary line drawn parallel to the equator, at 23°28′ S of the North Pole: between the North Frigid Zone and the North Temperate Zone

Arctic Circle in British English
noun: the imaginary circle round the earth, parallel to the equator, at latitude 66° 32′ N; it marks the northernmost point at which the sun appears above the level of the horizon on the winter solstice