Viratham in Tamil Hindu Brahmin Iyer weddings is a ritual that is performed separately by the bride and groom as part of the pre-wedding celebrations. By performing this ritual both bride and groom seek permission to start their married life. The viratham(fasting) is observed to get the blessings of the elders who have departed to the nether world. The main wedding starts only after this ritual is conducted and this is a more elaborate function for the groom than for the bride. Nowadays there are books available from which you can check out the viratham irukum murai (how to follow the viratham) in Tamil Brahmin Iyer weddings.

What Happens During Tamil Brahmin Iyer Pre-wedding Ritual Viratham
For the bride - A sacred thread called the Charadu will be tied to the wrist which is believed to keep the evil spirits away and is considered as protective armor

For the groom - The ritual begins with the bride's paternal aunt also called the Athai offering oil for bath and sweets to have after bathing before the viratham. Shaving kit and toiletries are included as traditionally he would not have shaven till then. 

• After shaving and taking bath the groom offers prayers to Indra, Chandra, Soorya, and Agni
• After the prayer, the groom will ask permission from his father to end his brahmacharya or bachelorhood. In the olden days, the groom had to seek permission from his Guru to get married. But in modern times, he takes permission from his father.
• The groom then gets ready for entering the Grihastha ashrama by giving up all his personal grooming items
• After this ritual, the bride and groom cannot leave the marriage venue until they become a married couple

The Significance
The bride and groom observe fasting for a good progeny and a happy married life. The Pallikai ceremony and a few other small rituals are performed along with this event.