A function that runs when something happens on your page, like a click, keypress, or form submission.
An event handler is a Function that springs to life when something specific occurs on your page. Events include clicks, mouse movements, keyboard presses, form submissions, and page loads. Each event can trigger a handler function.
You attach event handlers using addEventListener() or by setting properties like onclick. When the event happens, the browser automatically calls your function — this is the Callback pattern in action. Event handlers receive an 'event object' with details about what happened (which key was pressed, where the mouse was, etc.).
Event handlers are the bridge between user actions and code. They make pages interactive. Without them, your page would be static. Most of what happens in a web app is triggered by event handlers responding to user input.
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