A Page Title Notifier is a JavaScript feature that allows a webpage to notify users about changes in the page's title updates on the page when they are not actively focused on it. This is often used in applications like messaging apps, news websites, or real-time notifications, where the page's title updates to grab the user's attention, typically by modifying the content of the title (like adding an exclamation mark, count of unread messages, or a flashing indicator)