It can be made from ashes from burnt wood. It contains potassium carbonate, sodium carbonate and a few other chemicals.
Added to water, it makes the water very alkaline.
It can be used to process kernels of corn, just as Lime is. Lye in water causes the kernels of corn soaked in it to swell, loosening the hulls. The corn is then rinsed well to get rid of the Lye and the hulls.
The result is called Hominy.
Similar results could be achieved by using the chemical Lime. The taste difference probably would be minimal given that the product is washed thoroughly afterwards anyway.