15 days constitute a Fortnight, Pancha Dasa Ahani Pakshah

15 days is one Fortnight and is called a Paksha.

There are 2 types of Fortnight, Bright and Dark, Shukla Paksha and Krishna Paksha, Tad Shuklam Krishnascha.

Fifteen Days after Black Moon / New Moon – Bright Fortnight / Shukla Paksha

Fifteen Days after Full Moon – Dark Fortnight / Krishna Paksha