The *Kernel* is the core of Symfony2. The Kernel object handles HTTP

requests using all the bundles and libraries registered to it. See

:ref:`The Architecture: The Application Directory <the-app-dir>` and the

Firewall

In Symfony2, a *Firewall* doesn't have to do with networking. Instead,

it defines the authentication mechanisms (i.e. it handles the process

of determining the identity of your users), either for the whole

application or for just a part of it. See the

YAML

*YAML* is a recursive acronym for "YAML Ain't a Markup Language". It's a

lightweight, humane data serialization language used extensively in

chapter.