Pavan, you can configure the default interceptor stack to be used for your actions in a package using this syntax
Usually when we define a package in struts.xml, then we extend the struts-default package. That package contains a defaultStack which you can see
here. So if you don't specify a default interceptor stack for your package, then the defaultStack will be used. Please note that this only happens if you don't explicitly provide an interceptor stack for you action. So if a package contains an action which has no interceptor stack of its own, then the defaultStack will be used. But if an action has an interceptor stack of its own, then the defaultStack will not be applied on that action...