I'm confused. are , , and elements or nodes? what exactly defines nodes? what defines elements?

Nodes and elements can be defined differently in different subjects. In Geography, an element is defined by the basic components of the conceptual data model of the physical world. Elements consist of nodes. Nodes define points in space. In the computer science world and in the context of XML or HTML, a node is the smallest piece of text that has a semantic meaning. It is defined as part of the Document Object Model (DOM) for processing XML documents. An element, on the other hand, is part of the formal definition of a well-formed XML document.  It is everything from the element’s start tag to the element’s end tag.