Is Google App Engine an example of serverless? The user does not really think about servers, and the code is mostly written as event handlers. The abstraction is a bit leaky though, and you can tell that there are instances being spun up and down.
That buzzword means absolutely nothing.
The difference is that traditional PaaS like App Engine and Heroku imply a certain amount of lock-in (although this has gotten better over time), whereas Serverless is a more raw compute service that is no more locked-in than, say, EC2.