In Vedic astrology, Birth star or Janma Nakshatra or simply 'Nakshatra' is the name of the constellation in which the Moon was located at the time of the birth. Hence, it is often referred to as Lunar Mansion.
The word Nakshatra means "something eternal", or in Sanskrit "Naks"- translates to the sky and "shetra" referring to an area or a particular region, so together it means a specific area of the sky.
Other than Vedic Astrology, this phenomenon of classifying constellations based on the Moon is also seen in Persia, Arabia, Egypt, Babylonia, China under various terms like Manzil, Sieu, etc.
According to Vedic science, a full zodiac or the "sky map" is of 360 degrees. There are about 27 Nakshatras, categorized into 12 Rashis or Moon signs, with each constellation of 13 degrees and 20 minutes.
The nakshatras are classified on varied qualities, like Guna, animal, or other qualities like the Kama, (Sensual desires), Artha (Mental desires), Dharma (Principles), and Moksha (ultimate liberation).