Which desert is widely described as the driest non-polar desert in the world?

The desert widely described as the driest non-polar desert in the world is the Atacama Desert.

The Atacama stretches along northern Chile's Pacific coast, in a long, narrow zone west of the Andes. Its extreme dryness comes from several geographic effects working together: the cold north-flowing Humboldt Current, persistent high pressure over the Pacific and rain shadows created by both the coastal mountains and the Andes.

Some parts receive only around 1 to 2 millimetres of rain annually, and certain weather stations have recorded no rain for years. The Atacama is not uniformly lifeless, however. Coastal fog called camanchaca supports “fog oases,” while hardy plants such as tamarugo, llareta and various cacti survive where moisture is available.

The desert's Mars-like soils and exceptionally dry conditions have made it useful for testing planetary instruments and studying the limits of microbial life. Rare heavy rains can trigger floods and produce the spectacular “flowering desert,” when dormant seeds briefly bloom.

The Gobi, Mojave and Namib are also extremely arid, but they are not the standard answer to the non-polar-driest-desert description.