My take: Push Notifications means you get a message on your screen from a person or website you've been to before. Usually (not always) an "ad" to get you to do something more online, even tho' you're no longer on the sender's website. Unfortunately, many websites default to sending your push notifications automatically, and you have to take action to stop them. (You can set your browser to filter or block them.)
I see young folks staring at their cell screens almost continuously these days - swiping through their dozens of daily "push notifications", a few of which might actually be useful!
yeesh