Root : The topmost node in a tree is called root.
Leaf node: It refers to a node with no children.
Subtree: A portion of a tree, which can be viewed as a separate tree in itself is called a subtree.
Children of a node: The roots of the subtrees of a node are called the children of the node.
Degree of a node: It refers to the number of subtrees of a node in a tree.
Edge: A link from the parent to a child node is referred to as an edge.
Siblings/Brothers: It refers to the children of the same node.
Internal node: It refers to any node between the root and a leaf node.
Level of a node: It refers to the distance (in number of nodes) of a node from the root.
Depth of a tree: Refers to the total number of levels in the tree. The depth of the following tree is 4.