What can a business use to send messages to users who have already downloaded their app?

Push notifications are messages sent directly to a user's mobile device from an app they have installed, even when the app is not actively in use. This makes them an effective tool for re-engaging users who have already downloaded the app. Text messages are typically sent to a phone number and are not directly tied to app usage. Pull notifications are a less common term, but generally refer to information a user actively retrieves, rather than passively receives.