Which place is known as the roof of the world ?

Recently I have heard the term roof of the world somewhere and i knew people give this title to certain place. Where is such place and why it is called roof of the world and where exactly this place is located.
Recently I have heard the term roof of the world somewhere and i knew people give this title to certain place. Where is such place and why it is called roof of the world and where exactly this place is located.