What does Context Root mean?

I am deploying a simple web module to glassfish server.

The package name is test2.war.

The runtime deployment descriptor file sun-web.xml specifies the Context Root as below:

  <context-root>/myTest</context-root>

According to the Java EE 5 tutorial, A context root identifis a web application in a Java EE server. I expected that I should visit my site like below:

http://localhost:8080/myTest

But it turns out I still have to use:

http://localhost:8080/test2

So what's the purpose of Context Root? How to use it?