Handling background push notifications

I’m currently developing an app with ionic v1 and using ionic cloud services for push notifications. I’ve been trying to work with background notifications, however, in that guide there is an unknown object to me that I currently don’t know how to get.

push.on('notification', function(data) {
    // do something with the push data
    // then call finish to let the OS know we are done
    push.finish(function() {
        console.log("processing of push data is finished");
    }, function() {
        console.log("something went wrong with push.finish for ID = " + data.additionalData.notId)
    }, data.additionalData.notId);

Can someone explain what is that push object and how it’s retrieved so I can set the event handler?