Push notifications are subscriber based messages which can be received on PC, Mac, Android phones and tablets.
​
This is how their look like on Android mobile devices

PCs and MACs

Websites can send push notifications directly to people who've subscribed to receive notifications from their web browsers. 

They are sent via web browsers like Google Chrome, Firefox, Opera, Safari which means that your customers will receive them even if they are not on your web site. 

They allow you to send messages to your customers directly, wherever they are on the internet.