Html.Hidden() asp mvc 2

Im following the book ASP.NET MVC 2 by Steven Sanderson, and I don't understand the method helper Html.Hidden(), I mean, I don't know what does suppose to do. this is the specific call:

Html.Hidden("returnUrl", Request.Url.PathAn开发者_开发百科dQuery)

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It basically hides a value from user (visitor of page), but keeps it available when you do POST with your model afaik.