Binary tree
Also known as: BT
A binary tree is a tree where each node has at most two children (left and right). It is a special graph: connected, acyclic, rooted for most algorithm discussions.
Height can be $n-1$ when skewed or $\Theta(\log n)$ when balanced. Heaps and BSTs add order constraints on top of the binary shape.
Traversals: preorder, inorder, postorder (DFS styles), and level-order (BFS). See tree traversal.