A boomerang is a curved piece of wood used that was originally used by Australian Aborigines as a weapon or for sport. If you throw a boomerang right, it will travel around in a loop and come back to you.
Other cultures outside of Australia have also developed boomerangs, but theirs do not return when you throw them.
Pyongyang is the capital of North Korea. It has a population of around 2.5 million people.