Deserts are defined by their extreme aridity, receiving less than 10 inches (250 mm) of rainfall per year. They are characterized by:

* Low precipitation: This is the defining characteristic, with very little rain throughout the year.

* Sparse vegetation: Only plants adapted to drought conditions can survive, often with deep roots or specialized mechanisms for water storage.

* Wide temperature fluctuations: Days can be extremely hot, while nights can be very cold.

* Sandy or rocky soils: Lack of rainfall leads to poor soil development.

There are several types of deserts, including:

* Hot deserts: Located in the tropics, they are characterized by high temperatures and low humidity. Examples include the Sahara Desert in Africa and the Atacama Desert in South America.

* Cold deserts: Located in higher latitudes, they experience cold winters and hot summers. Examples include the Gobi Desert in Asia and the Mojave Desert in North America.

* Coastal deserts: These are found in areas with cold ocean currents that produce fog but little rain. An example is the Namib Desert in Africa.

While there are other biomes that experience periods of dryness, deserts are the most extreme and thus, the driest.