1. A tree in which each node has at most two subtrees, called the left and right subtrees of the node. At level h of a binary tree there is a maximum of 2^h nodes. A binary tree of depth d thus has at most (2^d+1 –1) nodes and one with n nodes has a minimum depth of log₂n.

The term binary tree is also used to describe any (ordered) tree of degree two.

2. Any data structure used to represent a binary tree. Each node is usually represented by pointers to the left and right subtrees as well as to the data value associated with the node. The binary tree can then be represented as a pointer to its root node.