Spookdroid:
Thanks for nothing. I asked what a push service is and you replied it is a push service. I don't know anymore than I did when before I read your answer, only another several minutes of my life wasted!
Hey, it's all good... just trying to help, and nope, I don't feel offended by your (rather harsh) remark. Just to be fair, you DIDN'T ask what a push service is... you asked what the app was. And that's what I responded
Now, you wanna know what a push service is? It's a service...that pushes things to your phone. No, really! It's a backround service that is lying dormant, awaiting 'commands' from another source (in this case, Samsung's servers). Once it gets the command to wake up and 'push' something to your phone, it becomes active and starts downloading something to your phone. In the case of e-mail apps, this lets you get a notification when you have new e-mail. In the case of messaging apps like Whatsapp, ChatON (which actually uses Samsung Push Service for it), and Line is that you get notified when you receive a new message and it downloads the message for you.
Why 'push'? Well, in the good ol' days of yore, smart phones were only getting smarter, but not quite so. There were no 'real time' notifications when you received an e-mail or a message (except for SMS/MMS, because those were handled by the carrier). So app developers responded to the users' need, or craving, to have instant gratification so they came up with polling services: Their apps would 'poll' their servers to check for new messages or items. Some apps still use this method because some services don't allow third-party apps to use them otherwise (like Facebook, or Twitter). You would set up at which intervals the app would wake up on its own, request the servers for new info, and download any new items if available. This became a big battery drain.
Enter Push services. Pioneered by the now-soon-to-be-defunct BlackBerry, they came up with a way to 'emulate' network messages to smart phones. You know how your phone is not constantly asking the carrier if you have a new phone call or if someone has sent you an SMS/MMS? You just get it instantly? Well, same idea but over data packets. The 'heavy lifting' would be done on the server side, and when you had new items waiting, the system would send the app a 'wake up' call, the app would then receive the new data, and then go back to sleep. Much more battery-efficient.
I hope that helps clear your doubt and if it doesn't, feel free to ask some more. Rude or not rude, I'll still answer

That's what we're here for
