A binary tree is a data structure that consists of nodes. Each node has at most two children, which are referred to as the left child and the right child. The root node is the topmost node in the tree, and the left and right children descend from it. Binary trees are used to implement data structures such as binary search trees, which are used for efficient searching and sorting.

There are several algorithms associated with binary trees. One of the most important is the traversal algorithm, which is used to visit all of the nodes in the tree in a specific order. There are three main types of traversal: pre-order, in-order, and post-order. Pre-order traversal visits the root node first, followed by the left child, and then the right child. In-order traversal visits the left child first, followed by the root node, and then the right child. Post-order traversal visits the left child first, followed by the right child, and then the root node.