Push notifications are a way to notify users of important events even if they are not using the application at the moment. They are great for letting users know that their package has been shipped, that their expense report has been processed or that they have received a new message.
Push Notifications build on the Web Push standard and ServiceWorkers. When configured, a ServiceWorker will be activated by an incoming push notification. It can then fetch updated data and display a notification to the user. The notifications are shown as normal system notifications on mobile or desktop.