Cusp (astrology) - Wikipedia In astrology, a cusp (from the Latin for spear or point) is the imaginary line that separates a pair of consecutive signs in the zodiac or houses in the horoscope. Because the solar disc has a diameter of approximately half a degree, it is possible for the Sun to straddle the cusp as it moves across the sky. When this occurs at the moment of birth such a person is said to be "born on …