What are the extra seats in the zodiac?

There is a Ophiuchus in the zodiac.

The twelve constellations, namely the zodiac, are astrological regions that describe the sun passing through the zodiac on the celestial sphere, including Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. Ophiuchus also passes through the zodiac, but it does not belong to the zodiac used in astrology. In astrology, the zodiac is defined as 1928. After the international astronomical union standardized the constellation boundary, there are 13 constellations on the zodiac.