Raksha Bandham (Hindu)

Also called Rakhi or Rakhi Purnima, this day celebrates the bonds between sisters and brothers. Sisters of all ages tie a sacred thread, called the rakhi, around the wrists of their brothers, symbolically protecting them, and in return they receive a gift from their brothers.  Traditionally, brothers also promise to take a share of the responsibility for ensuring the well-being of their sisters.

More information can be found here and here.