Definition of HTML "node" in DOM

A node is the representation of an object in the hierarchical model of a document. Types of nodes in a DOM include:

element nodes
attribute nodes
non-markup content - text, character data and whitespace
These nodes provide a model for content between the ">" ending one tag in a marked-up document and the "<" beginning another tag, which includes whitespace, text, character references and character data sections.
declarations
such as the xml declaration and the DOCTYPE declaration
processing instructions
such as the xml-stylesheet processing instruction
comments