What is a Node?
Nodes in Drupal, a single piece of content from a content type is called a node (regardless of what the content type is). Each node has a unique ID. This makes it easy for the website and developers to reference content by ID number rather than by page name or title which could change. Much of the reference to nodes and node IDs happen behind the scenes.
The node is found in the URL when signed in the back end of the CMS.