As an SEO professional, you need to understand what the DOM is, because it’s what Google is using to analyze and understand webpages.
The DOM is what you see when you “Inspect Element” in a browser. Simply put, you can think of the DOM as the steps the browser takes after receiving the HTML document to render the page.
The DOM is what forms from this parsing of information and resources. One can think of it as a structured, organized version of the webpage’s code.