Deserts are indeed characterized by very low precipitation, typically receiving less than 25 centimeters (about 10 inches) of rain per year. However, it's important to note that deserts can form in various geographical locations and under different climatic conditions, not just due to lack of rainfall. Here are some key points about desert formation:

1. Rainfall: The primary factor in desert formation is the limited amount of precipitation. This can be due to several reasons, such as:
- Being located in rain shadows of mountain ranges
- Being situated in subtropical high-pressure zones
- Being far from large bodies of water

2. Wind patterns: Many deserts are found in regions where prevailing winds blow dry air from continental interiors.

3. Ocean currents: Cold ocean currents near coastlines can lead to coastal deserts.

4. Latitude: Some deserts are found at specific latitudes, like the subtropics (e.g., Sahara Desert).

5. Altitude: High-altitude plateaus can experience desert-like conditions even with moderate rainfall due to low temperatures.

6. Human activity: In some cases, human practices can contribute to desertification of previously habitable areas.

Some examples of deserts formed primarily by lack of rainfall include:
- Sahara Desert in Africa
- Arabian Desert in Western Asia
- Mojave Desert in North America

Other deserts may be influenced more by factors like wind patterns or ocean currents:
- Atacama Desert in South America (influenced by cold ocean currents)
- Great Basin Desert in North America (high altitude)

In conclusion, while lack of rainfall is a crucial factor in desert formation, other geographical and climatic elements also play significant roles in creating these arid environments.