Wikipedia
The Madisar or Koshavam is a way in which the sari is worn mostly by the womenfolk of the Brahmin community in Tamil Nadu, India. In the olden days this was the customary style in which the sari was worn by a woman after her marriage. Today, to suit modern trends and yet accommodate traditions, the madisar is worn by women on select festive occasions and religious ceremonies. Normally saris are six yards in length but since the madisar is worn in a different style, one requires a nine-yard sari to wear it. It is a very important part of the Iyer and Iyengar culture. Both Iyer and Iyengar Brahmin wear madisars for all important occasions in their lives, starting with marriage, followed by Seemantham (form of a baby shower), all important Puja, and death ceremonies.
Iyers and Iyengars wear Madisars differently. Iyers drape the Pallu (the layer of sari which comes over one's shoulder) over the right shoulder while Iyengars wear it over the left shoulder.Conventionally, Madisar is maroon or red in colour, nowadays Madisar is being worn in other colours according to people's wishes.
Madisars are available in a variety of materials such as silk, cotton, cotton-silk blends, polyester-cotton blends, etc. These days a version of the madisar is also tied using the 6-yard sari. Though not as traditional, it is easier and more convenient to wear.