Raksha Bandhan or Rakhi is celebrated on a full moon day in the month of Sravan (August)

on this day brothers and sisters reaffirm their bonds of affection.

It is usually a festival of the Hindus, though today people from different religions participate as well.

Sisters tie colourful threads or rakhis on their brother's wrists. The brothers in turn promise to protect their sisters from all difficulties that may come her way.

There is no age barrier that is to say, that if, the brother is even younger than his sister in age he vows to protect her under all circumstances.

--Festivals of India