Leaf node is a concept in discrete mathematics. Nodes without children in the tree (that is, nodes with degree 0) are called leaf nodes, which are called "leaves" for short. A leaf refers to a node with a degree of 0, also known as a terminal node.

A child node is a node below the parent node. In the data model of database management, in the early hierarchical model and mesh model, if an attribute has a superior level, it is called its parent node; If there is no upper level, it has no parent node.