param element

It can be used with result,action or interceptor-ref element
1.With action element-To set an action property 
Used to pass value to an enclosing object.It holds a name attribute and its value defined inside tag
<action name=".........." class=".........">
 <param name="....property....">....value....</param>
</action>

2. With interceptor-ref element-->To exclude certain methods from invoking the enclosing interceptor


<interceptor-ref name="validation">
  <param name= "excludeMethods">input,back,cancel</param>
</interceptor-ref>


3.Used with result element--> To define location 


<result>/index.jsp</result>
is same as
<result>
 <param name="location">/index.jsp</param>