Lohri falls on the night before Maghi, around 13 January, at the end of the coldest fortnight. A bonfire is lit, sesame, gur, peanuts and popcorn are thrown into it, and people go round it.
Children go door to door singing the Dulla Bhatti song and are given gur, sweets or money. The song is about a sixteenth-century Muslim outlaw who rescued two Hindu girls and married them off himself, and it is sung by children who know nothing about him.
Lohri is traditionally celebrated most for a newborn son and for a newly married couple. That asymmetry, a whole festival organised around the arrival of boys, is the subject of a good deal of recent argument in Punjab, and a number of families now hold Lohri for daughters deliberately.
Punjab has among the most skewed child sex ratios in India. The festival did not cause that and it is a visible expression of the preference behind it.
The fire, the sesame and the gur belong to a winter solstice observance older than any of the stories attached to it.
Maghi the next morning is the Sikh observance, marking the forty at Khidrana, and the mela at Muktsar falls on it. The two days run as one occasion in most Punjabi households and they come from entirely different places.
It was specifically the festival for a son born in the past year, and the households with a new son bore the cost. That association is exactly the one the sex ratio problem is built on.
A number of families and organisations now hold Lohri for daughters deliberately, which is a small and pointed reversal of an old practice.