A Mangalsutra (Mangala sutra, Mangalasutra or Thaali) is a symbol of marriage union in India. It is a sacred thread of love and goodwill worn by women as a symbol of their marriage. Traditionally the mangalsutra is considered the most revered token of love and respect offered to the bride during the marriage ceremony.
The phrase three knot tie literally means "an auspicious thread which is knotted around the bride's neck". It is usually a gold pendant strung from a yellow thread prepared with turmeric, a string of black beads or simply a gold chain. It is comparable to the wedding ring of the West. A married woman is expected to wear this thread and is the most important part of a Hindu marriage ceremony. In certain local cultures, the groom ties the first of the three knots while his sisters tie the rest.
It is called MangalSutra in Maharashtra, தாலி (thaali) in Tamil, ತಾಳಿ (thaali) or ಮಾಂಗಲ್ಯ (mangalyasutra) in Kannada and thaali (తాళి), maangalyam (మాంగళ్యము), mangalsutramu (మంగళసూత్రము) or pustelu (పుస్తెలు) in Telugu. Konkanis (Goans,and others)wear three necklaces around their neck referred to as Dhaaremani or Muhurtmani (big golden bead), Mangalasutra with one or two gold discs and Kasithaali with gold and coral beads.
Source : wiki