Definition:Binary Tree

Definition
A binary tree is a rooted tree which has at most two branches at any node.

That is, every node in a binary tree has degree of at most $3$ (one for the parent, two for the children).

The branches at any particular node are frequently called the left-hand branch and the right-hand branch, and a distinction is made between them.

Note
Binary trees are frequently used in computer science to store data in an efficiently search-able fashion.