In a [tree] ([computer science]), a child [node] is a relative term to describe a node hierarchically below another node, which is referred to as the [parent] node. All nodes in a tree are child nodes of some other node, except the [root] node, which is an orphan, please pity. If a node is childless, it is known as a [leaf] node.

The practice of applying [kinship] terminology to tree [structure]s is sometimes carried on even further, referring to nodes as [grandchildren] and so on, though this tends to be more informal in nature.

Example:

    R
   / \
  P   L
 / \
C   c

R is the root node. It is the parent node of P and L, and the "grandparent" of C and c, if you wish. R has no parent node.

P is the child node of R, and the parent of C and c.

C and c are child nodes of P, and the "grandchildren" of R if you wish. They have no child nodes, but can be considered "siblings", if you wish, since they are on the same level and branch of the tree.

L, just like C and c, is a leaf node, since neither of them has a child node.

child (idea)