When you are born on a cusp you have the characteristics of both signs but in spite of this you still have only one Sun sign. The Sun could be in the very last or the first degree of the given sign but this doesn't actually matter. The Sun can't be in two signs at the same time.
The cusp is 29° - 0° of a sign. It should also be noted that any planet can be on a cusp. The Sun is on the cusp of a sign around the 20th - 223rd of a month. Consulting an ephemeris for the day of birth will clarify. It must be noted however that the Sun can only be in one sign at any given time, even if the traits of both signs are shown in the native.
To be born on a cusp means that you were born on the day that the Sun switches zodiac signs.
For example, if you were born on March 19th, at 11:45pm, you would be considered a Pisces. But because Aries, the next Sun sign, starts on March 20th at 12am, (15 minutes after March 19th @ 11:45pm), you are born so closely to the Aries sign that your personality and life will be influenced immensely by Aries traits, although you are still a Pisces.
Transition between the two - so influenced by both.
The Date December 23rd isn't considered to be a cusp. A cusp is between 29 degrees 59 minutes and 59 second of one zodiac sign and 0 degrees of the zodiac sign immediately after it; a cusp between Aquarius and Pisces for example.
cusp of magic your cancer and Gemini cusp
Cancer-Leo Cusp.
The cusp is the intersection where a planet moves from one sign to another. Planets within the last or beginning 5° of a sign are considered on the cusp and thus possess some traits of both signs. Most of the time "cusp" or "being born on a cusp" is used to refer to the Sun passing over this intersection.
It's a Leo-Virgo cusp; primarily Leo. A cusp is a sign which is technically one sign, but because of the day of birth, it displays traits of the other.
Technically: yes. It is a Capricorn-Aquarius Cusp; and it's about 50/50 each.
gemini/cancer
Usually if you are born on or one day either side of the 21st of a month, then you will be a cusp sign. You may take on traits of both signs of the months in question.
September 21st, is on the cusp of Virgo and Libra so even though it is classified as Virgo, if you feel you are better represented by the sign Libra, then that should be your sign.
Born 23rd June 1989 you are: Cancer on the cusp of Gemini in the western zodiac. It is important to look at Cancer first and then check Gemini for the mitigating circumstances. Woodpecker (no cusp) in the Amerind earth magic zodiac Year of the Snake in the Chinese zodiac.
Cusp birthdays refer to days when the Sun is transitioning from one sign to another. I.e. Jan 22 is considered a cusp birthday because on this day the Sun moves from Capricorn to Aquarius. When planets are transitioning to another sign they are said to be on the cusp of a given sign; carrying over traits from both signs. However a body can not occupy more than one sign. The Sun can only be in Capricorn or Aquarius on Jan 22. A native can not be born as a Capricorn/Aquarius.
Aries on the cusp of Taurus.