Deserts are the driest places in the world.
They get less than 25cm of rainfall in an entire year.
Deserts can be both hot and cold, it is the amount of rainfall that makes it a desert.
The largest hot desert in the world is the Sahara Desert, covering most of North Africa.
It is mostly made out of sand, with dunes (sand hills) reaching over 500 feet tall.
The temperature there can reach as high as 50 degrees.
The largest cold desert in the world is the Antartic Desert. Most people don't think it is a desert, but it hardly ever rains there which is why it is one.