Parent and child
The relationships between the various values are referred to as though they were part of a family tree. Each dimension value in a hierarchy (except the top-most value) has a parentvalue, which is the value directly above it in the structure. The dimension values directly below a parent are called its children.
Descendant and ancestor values
Each child value can also have children of its own, and so on. Multiple levels of dimension values that roll up to a common value are called descendants of that value, and the value itself is known as the ancestor of the descendent values.
This info will help during multiple level category management. I read this definitions while making multi level category manager in PHP for one project and helped me a lot. Before you make multi level category manager, you need to know what is parent, child, ancestor and descendant.