Symfony 2 is mainly used to create web application, however, sometimes you need to extend your app and need a command line tool to help perform tasks around the application. With symfony 1.4.x these were called tasks and it was possible to create a skeleton by using the symfony generate:task task.
While there's not a tool for it, Symfony2 does offer something called "Commands" as a sort of replacement. A basic skeleton of one is included with the framework, there's just no auto-generation tool for them (yet). The basic one, TestCommand.php, shows you how to set up a command's name, arguments and some parameter mapping. The post includes this code example and how it looks when called from the command line.