Subscribers are the store visitors who have given you the permission to send them notifications on their mac, desktop, laptop, mobile or any other device with a browser.
Here's how these visitors grant you permission to send them push notifications.
When someone visits your store for the first time, they'll see a browser prompt as shown below. As soon as they click on 'Allow', you can start sending them notifications.
Gone is the hassle of asking for email IDs, replaced with just one click of a button!