The Great Blight is a corruption of the land that lies north of all the land, even extending beyond Shayol Ghul. It eastwards across the northern boundaries of both the Aiel Waste and Shara as well, and some theorize that it even extends across the ocean floor (giving rise to the body of water known as the Dead Sea) to the Seanchan continent, where it is known as the Lesser Blight.
The Great Blight is rotten and bare land, created by the influence of the Dark One over the world. All the earth has turned to dust and very few flora live here. It is a very dry land, as no lakes have been reported by survivors of this place. This makes it very uninhabitable for people. It also has several mountains. They are very high and few people, if any, ever climb them.
It is revealed by Graendal that the red color of the soil is the result of large quantities of iron present in it. It is also revealed that the climate of the Blight is hot and dry, though the temperature gets colder the further north one goes.
The Great Blight lies north of the Westlands, the Aiel Waste, and Shara. The Mountains of Dhoom separate the Westlands from it. The Aiel Waste just flows over to the Blight, but Shadowspawn will rarely enter the Waste. It is unknown if there are mountains separating Shara from the Blight, due to the secretive nature of this nation.
Shayol Ghul also lies in the Great Blight. Here, the Pattern is at its thinnest and the influence of the Dark One is the greatest. It is a very high mountain whose top is shrouded in the clouds and where the temperature is very low. Without the aid of the One Power to get here, it is almost impossible to travel to Shayol Ghul.
For thousands of years, Aiel male channelers journeyed to the Blight to fight the Dark One as a matter of toh. For thousands of years, society assumed that these men died- either to the taint or Shadowspawn. However, as Tarmon Gai'don approaches, red-veiled Aiel have begun to invade from the Blight. They appear as men, but something is wrong with them.
A warped civilization lives within the Blight. Humans congregate in a place dis-affectionately dubbed "the Town."
Although it is a bare land, the Great Blight is home to several creatures and some weird plants. Most of them were created by Aginor in the War of Power.
The most well-known inhabitants of the Blight are Shadowspawn, including Trollocs, Myrddraal, and Worms. No humans live in the Blight because of the harsh conditions.
Sticks are animals that look like branches of a tree, but try to strangle people who walk by them. The trees seem fleshy, rather than woody like the trees in the south.
This information is collected from the Wheel of Time Wiki located at http://wot.wikia.com/wiki/Great_Blight.