Weaning is the process of gradually introducing a mammal infant to what will be its adult diet and withdrawing the supply of its mother's milk.
The process takes place only in mammals, as only mammals produce milk. The infant is considered to be fully weaned once it no longer receives any breast milk (or bottled substitute).
Read more about Weaning: Weaning in Human Infants, Weaning Conflict, Age of Weaning, Weaning in Other Mammals