You don't answer my question which is either because you don't have a definition but then I don't know how you can write of "a different definition" or you don't want to tell me your definition.
Moreover, I don't see how you conclude from my question "What is your definition of firewall...?" that I think NAT routers fall short of whatever you think I think they should fall short of. Nor I said anything about being right or wrong. Since when people have to make such a huge fuss about a simple, plain question?
If you don't care about my definition, well whatever, I was just curious of your definition and thus I asked you. But, well, obviously you don't have one or don't want to tell us your definition which to me means the same in the end: you don't have one...
Gerald