Onload refers to the event or process that occurs when a web page or a specific element within a page has fully loaded in a user's browser. In web development, the "onload" event is commonly used in JavaScript to trigger functions or scripts once all resources such as images, scripts, and stylesheets are completely loaded. This ensures that any code dependent on the full availability of page content executes at the appropriate time, improving user experience and preventing errors related to missing elements.