Which of the following terms describes a tree node that is the first node along a path?

The term that describes a tree node which is the first node along a path is the "root." In the context of tree data structures, the root is significant because it serves as the starting point from which all other nodes are accessible. It does not have a parent and is the topmost node within the hierarchy of the tree.

Understanding the structure of a tree is essential for grasping concepts such as tree traversal and manipulation. The root node is foundational, as it enables navigation to all other nodes through various paths. The hierarchical nature of trees means that every other node can be reached by following a path that originates at the root.

In contrast to the root, other terms like "child" and "leaf" refer to different aspects of the tree. A child is a node that is directly connected to another node when moving down the tree, while a leaf is a node that has no children, indicating it is at the end of a path in the tree. A subtree represents a smaller tree structure that includes a node and all its descendants. However, neither of these terms describes the primary, starting node, which is specifically defined as the root.