What is the name of the latitude line located at 66.5 degrees north of the equator?

The latitude line located at 66.5 degrees north of the equator is indeed known as the Arctic Circle. This line marks the latitude at which, during at least one day a year, there is a phenomenon called the midnight sun, where the sun does not set, and during another day, there is polar night, where the sun does not rise. The Arctic Circle is significant in understanding climate patterns, ecosystems, and the behavior of polar regions, as it delineates the boundary of the area that experiences these extreme daylight variations due to the tilt of the Earth's axis.