There is no universally accepted definition of "child labour". Varying definitions of the term are used by international organizations, non-governmental organizations, trade unions and other interest groups. Writers and speakers don’t always specify what definition they are using, and that often leads to confusion. Wikipedia encyclopaedia defines child labour as the employment of children at regular and sustained labour. This practice is considered exploitative by many countries and international organizations. Child labour was utilized to varying extents through most of history, but entered public dispute with the beginning of universal schooling, with changes in working conditions during industrialization, and with the emergence of the concepts of workers' and children's rights. Not all work is bad for children. Some social scientists point out that some kinds of work may be completely unobjectionable — except for one thing about the work that makes it exploitative. As Unicef’s 1997 State of the World’s Children Report puts it, "Children’s work needs to be seen as happening along a continuum, with destructive or exploitative work at one end and beneficial work - promoting or enhancing children’s development without interfering with their schooling, recreation and rest - at the other. And between these two poles are vast areas of work that need not negatively affect a child’s development." Other social scientists have slightly different ways of drawing the line between acceptable and unacceptable work. Who then is a child? International conventions define children as aged 18 and under. Individual governments may define "child" according to different ages or other criteria. " A "child" is not necessarily delineated by a fixed age. Social scientists point out that children’s abilities and maturities vary so much that defining a child’s maturity by calendar age can be misleading.