Children become malnourished when they do not receive the adequate nutrients their bodies require to resist infection and maintain growth. When nutritional deficiencies become too significant, a child will begin to 'waste' - to consume his/her own tissues to obtain needed nutrients. Wasting is a sign of acute malnutrition.
In some regions of the world, such as in Africa's Sahel, wasting is particularly frequent among children during the 'hunger gap' period, between harvests.
The World Health Organization (WHO) estimates that there are 20 million young children with severe acute malnutrition at any given point in time.
(MSF via China.org.cn December 2, 2008)