A wadi, which means « river » in arabic, is a stream or river in North Africa and other sub-desert areas. These are water courses with a very irregular hydrological regime.
They mainly occur in endoreic regions, and get their water from rare but heavy rainfall. Wadis are most often totally dry but can be affected by strong floods, which sometimes changes the whole river bed.
Around wadis, many human communities settle (permanently or seasonally), because of the presence of both water (surface or underground) and tree or shrub cover that provides wood-fire, shelter and fodder.