Janai is a sacred circular cotton thread worn across the chest by the Brahmin and Chettri males.
This thread is given to males once they go through a long and impressive religious ceremony called Bratabandhan. Bratabandhan is a ritual that makes a boy ready to be a man. A boy must go through this rite of passage before they are 16 years old and usually when they are at odd number age like, 3, 9, 11 and so on.
Males after receiving Janai during this ritual continue to wear it in such a way that it diagonally dangles from the left shoulder crossing to the other side of a torso.
These males change their Janai yearly during Janai Purnima Festival, loosely translating to an auspicious Full Moon day to change Janai.
In Sanskrit, it’s called Uapanaya, yagnyopavita or janeu.