Root : node without parent (A)
Internal node : node with at least one child (A, B, C, F)
External node (leaf) : node without children (E, I, J, K, G, H, D)
Ancestors of a node : parent, grandparent, ....
Depth of a node : number of ancestors (I → 3 (F, B, A))
Height of a tree : max depth of any node (3, it depends on the book. Some would count the node itself in, so it'd be 4)
Descendant of a node : child, grandchild, .... (B → E, F, I, J, K)
Subtree : tree consisting of a node and its descendants (A, C, D, G, H cant be a subtree bc it doesnt include A's all descendants)
Ordered tree : when it has a meaningful linear order among the children of each node
