The Documentation Object Model is a interface for web documents. It represents the page so that programs can access the structure, style, and content.
DOM (Document Object Model) is a set of specifications recommended by W3C (World Wide Web Consortium) to define an API (Application Programming Interface) for valid HTML and well-formed XML documents.
The DOM implementation interface represents an object providing methods which are not dependent on any particular document.
In summary the DOM is built using multiple APIs that work together. The core DOM defines the entities describing any document and the objects within it. This is expanded upon as needed by other APIs that add new features and capabilities to the DOM. For example, the HTML DOM API adds support for representing HTML documents to the core DOM, and the SVG API adds support for representing SVG documents.