struts action mapping action input attribute

I am a noob when it comes to Java and Struts ( I feel like .Net boy in Java world ).

What is the input attribute on the action element used for? So in the example below the input is someinput.jsp.

<action path="/somepath" 
        type="SomeAction" 
        name="SomeForm" 
        scope="session"
        input="someinput.jsp">