DOM

When you make an HTTP request (visit URL or click a link) the browser will download a copy of that file. It will then read it over and construct its own version of that HTML page.  Think of it as a JavaScript Object. A bunch of little collections of key:value pairs that describe the page structure and content – so that the browser can render the page – and also so that YOU can interact with it.

“The Document Object Model” is quite a mouthful, so – most people just call it “The DOM” – or when referring to parts of it, “DOM.”