Thaipoosam is considered as the most important festival that is celebrated in Pazhani a pilgrim in India for Lord Muruga.  It derived its name from the day it is celebrated. Thai is one of the tamil months and poosam is one of the stars. So this festival is celeberated during full moon on the month of thai(Mid jan- Mid feb) and on poosam star. The story behind this is Goddess parvathi gifted his son a lance to demonish a demon named Tharakasuran. And he was vanquished by Lord Muruga on this day. So this a celebration for the victory of good over evil.  The devotees pray to the lord and when it is answered they pierce any part of their body with metal skewers and take kavadis (paal kavadi, pannir kavadi, etc) to thank the lord. We make paanagam a drink and sweet thatta payaru(Cow peas) sundal and offer it to God. This year it falls on Jan 31st

The links to these recipes are:

Thatta payaru Sundal

Paanagam