A push notification is a message that pops up on a mobile device.
Push notifications look like SMS text messages and mobile alerts, they reach users who have installed your app.
They can do a lot of things;
for example,
-- they can show the latest sports scores
-- get a user to take an action, such as downloading a coupon
-- or let a user know about an event, such as a flash sale.
App publishers can send them at any time;
-- users don't have to be in the app or using their devices to receive them.
Each mobile platform has support for push notifications
-- iOS
-- Android
-- Fire OS
-- Windows
-- BlackBerry
each will have their own services.