Push notifications are messages sent directly to a user's device from an app or website, even when the app is not actively in use. They are designed to provide timely updates, reminders, or alerts, helping users stay informed about important information or events. These notifications can appear on smartphones, tablets, or computers, and can include text, images, or action buttons. Users can usually customize their preferences, choosing which notifications to receive and how they want to be alerted, enhancing their overall experience with the application or service.