What is a defining characteristic of a binary tree?

A binary tree is defined by the property that each node can have at most two children. This structure allows for various traversal methods and algorithms that operate efficiently due to the limited number of child nodes. The two children typically are referred to as the left child and the right child, forming a clear and manageable hierarchy.

This characteristic is crucial because it defines how other data structures and algorithms, such as binary search trees and heaps, are constructed and manipulated. The constraint of having only two children simplifies the implementation of various operations like searching, inserting, and deleting nodes.

While other tree structures may allow nodes to have many more children, the limitation to two children in a binary tree makes it a foundational concept in computer science, especially in areas involving hierarchical data representation and algorithm design.