.. glossary::
:sorted:
Distribution
A *Distribution* is a package made of the Symfony Components, a
selection of bundles, a sensible directory structure, a default
configuration, and an optional configuration system.
Dependency Injection
The Dependency Injection is a design pattern highly used in the Symfony Framework.
It encourages loosely coupled and more maintainable architecture of an application.
The main principle of this pattern is that it allows developers to *inject* objects
(also known as services) in other objects, generally passing them as parameters.
Different levels of coupling between these objects can be established
depending on the method used to inject objects together.
The Dependency Injection pattern is the more often associated
to another specific type of object: the :doc:`/book/service_container`.
Project
A *Project* is a directory composed of an Application, a set of
bundles, vendor libraries, an autoloader, and web front controller
scripts.
Application
An *Application* is a directory containing the *configuration* for a
given set of Bundles.
Bundle
A *Bundle* is a directory containing a set of files (PHP files,
stylesheets, JavaScripts, images, ...) that *implement* a single
feature (a blog, a forum, etc). In Symfony, (*almost*) everything
lives inside a bundle. (see :ref:`page-creation-bundles`)
Front Controller
A *Front Controller* is a short PHP script that lives in the web directory
of your project. Typically, *all* requests are handled by executing
the same front controller, whose job is to bootstrap the Symfony
application.
Controller
A *controller* is a PHP function that houses all the logic necessary
to return a ``Response`` object that represents a particular page.
Typically, a route is mapped to a controller, which then uses information
from the request to process information, perform actions, and ultimately
construct and return a ``Response`` object.
Service
A *Service* is a generic term for any PHP object that performs a
specific task. A service is usually used "globally", such as a database
connection object or an object that delivers email messages. In Symfony,
services are often configured and retrieved from the service container.
An application that has many decoupled services is said to follow
a `service-oriented architecture`_.
Service Container
A *Service Container*, also known as a *Dependency Injection Container*,
is a special object that manages the instantiation of services inside
an application. Instead of creating services directly, the developer
*trains* the service container (via configuration) on how to create
the services. The service container takes care of lazily instantiating
and injecting dependent services. See :doc:`/book/service_container`
chapter.
HTTP Specification
The *HTTP Specification* is a document that describes the Hypertext
Transfer Protocol - a set of rules laying out the classic client-server
request-response communication. The specification defines the format
used for a request and response as well as the possible HTTP headers
that each may have. For more information, read the `HTTP Wikipedia`_
article or the `HTTP 1.1 RFC`_.
Environment
An environment is a string (e.g. ``prod`` or ``dev``) that corresponds
to a specific set of configuration. The same application can be run
on the same machine using different configuration by running the application
in different environments. This is useful as it allows a single application
to have a ``dev`` environment built for debugging and a ``prod`` environment
that's optimized for speed.
Vendor
A *vendor* is a supplier of PHP libraries and bundles including Symfony
itself. Despite the usual commercial connotations of the word, vendors
in Symfony often (even usually) include free software. Any library you
add to your Symfony project should go in the ``vendor`` directory. See
:ref:`The Architecture: Using Vendors <using-vendors>`.
Acme
*Acme* is a sample company name used in Symfony demos and documentation.
It's used as a namespace where you would normally use your own company's
name (e.g. ``Acme\BlogBundle``).
Action
An *action* is a PHP function or method that executes, for example,
when a given route is matched. The term action is synonymous with
*controller*, though a controller may also refer to an entire PHP
class that includes several actions. See the :doc:`Controller Chapter </book/controller>`.
Asset
An *asset* is any non-executable, static component of a web application,
including CSS, JavaScript, images and video. Assets may be placed
directly in the project's ``web`` directory, or published from a :term:`Bundle`
to the web directory using the ``assets:install`` console task.
Kernel
The *Kernel* is the core of Symfony. 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
:doc:`Internal Events Reference </reference/events>`.
Firewall
In Symfony, 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
:doc:`/book/security` chapters.
YAML
*YAML* is a recursive acronym for "YAML Ain't a Markup Language". It's a
lightweight, humane data serialization language used extensively in
Symfony's configuration files. See the :doc:`/components/yaml/introduction`
chapter.