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Depending on the business environment or studying disciplines as neurology, networking, telecommunication or distributed systems the meaning of node differs, but generally it represents a point where more lines intersect or branch out. Nodes belong to trees and a tree can be defined locally as a collection of nodes (starting at a root node), where each node is a data structure consisting of a value, together with a list of nodes named "children" with the constraints that no node is duplicated. A tree can be defined abstractly as a whole (globally) as an ordered tree, with a value assigned to each node. Both these perspectives are useful: while a tree can be analyzed mathematically as a whole, when actually represented as a data structure it is usually represented and worked with separately by node (rather than as a list of nodes and an adjacency list of edges between nodes, as one may represent a digraph, for instance). For example, looking at a tree as a whole, one can talk about "the parent node" of a given node, but in general as a data structure a given node only contains the list of its children, but does not contain a reference to its parent (if any).http://en.wikipedia.org/wiki/Tree_%28data_structure%29