Amazon uses a hierarchy of nodes to organize its items for sale. Each node represents a collection of items for sale, such as Harry Potter books, not the items themselves. Amazon calls the nodes, browse nodes because the customer can browse through the nodes to find the collection of items that interests them. For example, the customer might be interested in the browse nodes Literature & Fiction, Medicine, Mystery & Thrillers:, Nonfiction:, or Outdoors & Nature.
Browse nodes are related in a hierarchical structure; each browse node can be a leaf node or a parent node. A leaf node has no children nodes, a parent node does, as shown in the following figure.
The figure is representational in nature and should not be construed to be the real browse node hierarchy used by Amazon.
As you can see in this example, the different levels of the hierarchical tree of nodes provides an organizational principle that is used to catalog and find items. The nodes progress from general to specific. For example, a top level browse node might be "Shoes." It's child browse nodes might be "Men's Shoes," "Women's Shoes," and "Children's Shoes." Child browse nodes are subsets of the parent's product category. Navigating down the tree refines the search for items from the general to the specific. Going up the tree generalizes the search from the child browse node toward the root node.
A node is a basic unit used in computer science. Nodes are devices or data points on a larger network. Devices such as a personal computer, cell phone, or printer are nodes. When defining nodes on the internet, a node is anything that has an IP address. Nodes are individual parts of a larger data structure, such as linked lists and tree data structures. Nodes contain data and also may link to other nodes. Links between nodes are often implemented by pointers.
Taken from https://en.wikipedia.org/wiki/Node_(computer_science)