Literally meaning "side",. a paksha is the period either side of the Full Moon Day (Purnima). A lunar month in the Hindu calendar has two fortnights, and begins with the New moon, (Amavasya). The lunar days are called tithis and each month has 30 tithis, which may vary from 20 – 27 hours. A paksha has 15 tithis, which are calculated by a 12 degree motion of the Moon. The first fortnight between New Moon Day and Full Moon Day is called Shukla Paksha, the period of the brightening moon (waxing moon), and the second fortnight of the month is called Krishna Paksha, or the period of the fading moon (waning moon). Nimach Panchang begin new lunar month from first day of Krishna Paksha while Gujarat Panchang begin new lunar month from first day of Shukla Paksha.
In Vedic astrology when a person does a prasna (a question chart) and the planet Venus indicates the time period, the event referred to in the answer will happen in a pakṣa (fortnight) from the time the question was asked.