The Document Object Model (DOM) is a programming interface for HTML and XML documents. It provides a structured representation of the document as a tree structure where each node corresponds to part of the document, such as an HTML tag. This allows programming languages like JavaScript to interact with and manipulate web pages.

In the context of a web browser, the DOM is created when a web page is loaded. The browser reads the HTML file and creates a DOM tree structure in memory. This tree structure can then be manipulated by JavaScript to dynamically change the contents of the web page.