While being logged in to some target system, the victim visits the adversarys' malicious site which displays a UI that the victim wishes to interact with. In reality, the iFrame overlay page has a transparent layer above the visible UI with action controls that the adversary wishes the victim to execute. The victim clicks on buttons or other UI elements they see on the page which actually triggers the action controls in the transparent overlaying layer. Depending on what that action control is, the adversary may have just tricked the victim into executing some potentially privileged (and most undesired) functionality in the target system to which the victim is authenticated. The basic problem here is that there is a dichotomy between what the victim thinks they are clicking on versus what they are actually clicking on.