How is push notification different from an SMS or a call? I don't have all of them on vibration, they don't all have the same importance to me but mostly it's

How is push notification different from an SMS or a call? I don't have all of them on vibration, they don't all have the same importance to me but mostly it's just another way of communication. When I receive an email, I wan't to know it, when someone contact me on Skype or Facebook, I wan't to know it too. If I don't wan't to be disturb, I just press volume down and the vibration is off.