This word is used to describe the relationship between two opposite signs of the Zodiac. The polar sign is the one at 180 degrees in opposition. They are in opposition, but the polarity relationship is a particular dynamic. Opposites attract, and the polar signs have a natural affinity based on the potential to balance each other out.
The polar signs are: Aries and Libra; Taurus and Scorpio; Gemini and Sagittarius; Cancer and Capricorn; Leo and Aquarius; Virgo and Pisces.