Street children is a term for children experiencing homelessness who live on the streets of a city. Homeless youth are often called street kids and street youth; the definition of street children is contested, but many practitioners and policymakers use UNICEF's concept of boys and girls, aged under eighteen years, for whom "the street" (including unoccupied dwellings and wasteland) has become home and/or their source of livelihood, and who are inadequately protected or supervised. Some street children, notably in more developed nations, are part of a subcategory called thrownaway children who are children that have been forced to leave home.