Push notifications are pop-up windows with information on the screen of a mobile device sent only to users who have agreed on receiving notifications. The purpose of «Notification» is to provide information. The use of push notifications in a mobile device implies that the technology does not require opening applications on the mobile device to receive a message. It allows a mobile device to receive and display text messages even when the device screen is locked and the application sending the notification is closed. Notifications most often appear from a sliding notification panel at the top of the screen, as well as on the lock screen.
The concept of push notifications has reached its peak of popularity after Apple launched the Apple Push Notification Service (APNS) for sending notifications to mobile devices running iOS 3. Later Apple implemented push notifications for OS X and Safari browser.