[sclug] Firewall question

[Neil Haughton]

This is not specifically a Linux question, but there seem to be a lot of
knowledgable networking people lurking here so I'm going to take a punt.

What is the difference between a conventional 'firewall' and an
'application firewall'? I've read the wikipedia page and am none the wiser.
I guess that an app firewall concentrates on traffic for a specific app,
but does the application itself (I'm thinking a web app) need to know about
the app firewall, or provide special hooks or anything like that? Can I
take an arbitrary web app, for example, say "FooApp", and shove an
arbitrary app firewall, say "Bar App Firewall 2013", in front of it, and
with suitable configuration expect the app firewall to protect the web app?

TIA.