What is an App Server?

I recently came across an interesting article on TSS aptly titled "What is an App Server?"

The traditional mindset has been, App Server = J2EE App Server, but that is changing now. As mentioned in that article,"an application server provides an environment where applications can run, no matter what the applications are or what they do"

Some people have been questioning whether it is correct to call WSAS an App Server since it does not support any of the JEE(J2EE) specs. This article on TSS should provide good answers to their questions.