Max asked: Is a smartphone an embedded system? It's not exactly dedicated to anything, but it's also not a PC...
Actually, IMO a smart phone is a PC. Yes, it has a ridiculously tiny screen (though better resolution and more colors than an Osborne 1) and limits what devices it lets you talk to, but those are details. Take a look at the Motorola Atrix smart phone, which you could plug into an Atrix Lapdock which then converted your phone into a laptop computer, using the phone to provide cellular data networking.
A "feature phone" that does not allow you to add your own programs is an embedded system. As soon as you can start running your own programs (or those purchased from 3rd parties), it's pretty much the same functionality as a PC.
Is a tablet a PC? Aren't most tablets just smart phones in a larger, easier-to-design package, with the voice communications module deleted?
How about this? "An embedded system is a product that uses a computer to provide its functionality by running a single program loaded into it by the manufacturer. Even though an embedded system contains a computer, you can't run your own program on it."
Unless your want to hack it, of course... whoops, this is my floor.
I forget who said this: "Designing embedded systems is a profession that's impossible to explain to your mother."