In the DOM, all document parts are organized in a hierarchical tree-like structure consisting of parents and children. These individual parts are called Nodes. The Node interface is an abstract base class, so there is no such thing as a plain Node object. Look at some of the most used properties nodeType, parentNode, childNodes, firstChild, lastChild, previousSibling, nextSibling, and attributes.
The DOM Node interface is an abstract base
class upon which many other DOM API objects are based, thus letting those object types
to be used similarly and often interchangeably. As an abstract class, there is
no such thing as a plain Node object. All objects that implement
Node functionality are based on one of its subclasses. Most notable are
Document, Element, and DocumentFragment.
In addition, every kind of DOM node is represented by an interface based on
Node. These include Attr, CharacterData
(which Text, Comment, CDATASection and
ProcessingInstruction are all based on), and DocumentType.
In some cases, a particular feature of the base Node interface may not
apply to one of its child interfaces; in that case, the inheriting node may
return null or throw an exception, depending on circumstances. For example,
attempting to add children to a node type that cannot have children will throw an
exception.
Source: Mozilla, https://developer.mozilla.org/en-US/docs/Web/API/Node
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