Push notifications are messages sent directly to a user's device, typically from a mobile app or web service. They serve to inform users about updates, promotions, or important information, enhancing user engagement and retention. By appearing on the device's home screen, they encourage immediate interaction. These notifications can be personalized based on user preferences and behaviors, making them a powerful tool for businesses. They can be used to drive traffic to apps, remind users of events, or provide timely information, ultimately improving the overall user experience and fostering a connection between the user and the service.