Here's some text I wrote for use elsewhere that might be good material to incorporate:
...the word "node" is derived from the Latin word for "knot" and it came into internet and computer terminology from a branch of mathematics called graph theory. A "graph" is an abstraction, an arrangement of any set of things into a web or a tree (note that this meaning of "graph" has nothing to do with "graphics" and is completely different from what is often called a "bar graph", which is simply a chart that graphically displays data). A junction or point in the web is called a "node" or a "vertex" and the lines between the nodes are called "edges".
A taxonomy, a web site's sitemap, the folder system on your computer's hard drive, and a set of nested user groups (only in a system that allows nesting of user groups, of course) can all be regarded as a tree type of graph (a tree graph is technically referred to as an "acyclic directed graph".) Examples of the more general web type of graph would be a computer network consisting of many interconnected computers or even better the lymphatic system of the human body; the edges of the lymphatic system are called "lymph vessels" and the places where the lymph ducts meet together are called "lymph nodes". (Though I should point out that in English, biology and physics adopted the word "node" independently of mathematics and it often simply means a "nodule" or "a lump of something" rather than being a node in a graph or system. That's also the meaning of "node" when you're talking about the the midpoints between peaks and valleys of a sine wave or the projections on the shape of a wave function of an atom in quantum physics.)