Answer 1

# I ROOT (root is also an INTERNAL NODE, unless it is leaf)
# / \
# I I INTERNAL NODES
# / / \
# o o o EXTERNAL NODES (or leaves or terminal node or non-internal)

# Internal node may mean: Nodes which are not leaves
# Terminal node may mean: Leaf node, a node of a tree data structure that has no child nodes.
# Non-Internal node may mean : Leaf node

I understand it as above