Push Messages or Push Notifications are notifications from an app that display while that app is not actively in use. They are handled by a device’s operating system and typically appear on the lock screen. In essence, a push notification is a brief message or alert that is sent through an app to everyone who has enabled the receipt of these messages.
When a user taps a Push message, it launches the app. (For progressive web apps, push messages currently work for Android devices but not for iOS devices.)
Alternately, “In-app” messages appear in an open app. They drop down from the top of the display (after a selected delay) when a user opens an app and will stay until dismissed or selected.
When selected, an in-app message will perform an action within the app. For example, an in-app message prompting an app install might link to a microsite with directions on how to do so.
In-app messages work on both iOS and Android.