In html, there are various events which represents that some activity is performed by the user or by the browser. The change in the state of an object is known as an Event. When java script code is included in HTML, js react over these events and allow the execution. This process of reacting over the events is called Event Handling. When the user clicks a button, that click too is an event. Other examples include events like pressing any key, closing a window, resizing a window, etc.