The DOM represents a document with a logical tree. Each branch of the tree ends in a node, and each node contains objects. DOM methods allow programmatic access to the tree; with them you can change the document's structure, style, or content. Nodes can also have event handlers attached to them; once an event is triggered, the event handlers get executed.
The Document Object Model (DOM) connects web pages to scripts or programming languages by representing the structure of a document—such as the HTML representing a web page—in memory. Usually that means JavaScript, although modelling HTML, SVG, or XML documents as objects is not part of the JavaScript language, as such.