tree
n. a type of graph in which there is only one path between any pair of nodes; the graph is undirected and has no cycles. In computer programming, a rooted tree represents a type of ranked nonlist data structure consisting of separate nodes linked in a parent–child hierarchy, with every node, other than the root node, having a single parent. Nodes that share a parent are sibling nodes, and a node with no children is called a leaf node. This data structure is commonly used in database programming to represent hierarchical data and to facilitate search algorithms.