What is an alert in Selenium?
An alert is an element of the page that Selenium can recognize and interact with. Just like you can understand the words on this page, Selenium understands the tags and design elements of this page. A button, for example, is an alert to Selenium: it has a certain color, size, and text on it. That’s what you’re telling Selenium to find when you write your code.
Learn more: Selenium Alert & Popup Window Handling: How to Handle?