Raksha Bandhan (Hindi: रक्षाबंधन, the bond of protection), or Rakhi (Hindi: राखी), is a festival primarily observed in India, which celebrates the relationship between brothers and sisters.It is also called 'Rakhi Purnima' in certain parts of India, like south. The festival is observed by Hindus, Jains and Sikhs. The central ceremony involves the tying of a rakhi (sacred thread) by a sister on her brother's wrist. This symbolizes the sister's love and prayers for her brother's well-being, and the brother's lifelong vow to protect her.The festival falls on the full moon day (Shravan Poornima) of the Shravan month of the Hindu lunisolar calendar.

http://en.wikipedia.org/wiki/Raksha_Bandhan