This will only work when you navigate to another JSP by a <form> which has this field embedded.
E.g. page1.jsp:
<form action="page2.jsp">
    <input type="hidden" name="foo" value="bar">
    <input type="submit">
</form>
And page2.jsp:
<p>Hidden value: ${param.foo}</p>
That's all. It won't work when you navigate by a link <a> or submit another form where the hidden field is not included.
(the ${param.foo} does effectively the same as out.print(request.getParameter("foo")), only in a less vintage and ugly manner. See also How to avoid Java code in JSP)