In the words of another, Robert J. Belton, Department of Fine Arts, Okanagan University College.  From his on-line resource Words of Art:

MEDIATION: A fundamental conception in postmodernism is that nothing exists in an innocent state and that nothing can be understood objectively because everything is mediated by all manner of intervening mechanisms. Social behaviour, for example, cannot be objectively assessed because the observer is either a member of the observed group, in which case s/he is subject to the same taboos of collective consciousness, or s/he is not a member of the observed group, which thus pollutes the observed behaviour. Similar assertions are current in quantum physics, where the presence of an observer or an observer's instrument affects the result of the investigation. The analogy in artwriting is that the meaning of an artwork is in part determined by the institutional mechanisms which mediate our experience of it (see critique of institutions). Native artists, for example, have drawn attention to the mediation of museums, which rip ethnographic artifacts from their original context and replace their genuine social meanings with depoliticized aesthetic ones. Mediation is now discussed in nearly every discipline. Even in works directed at popular audiences, one can find acceptable definitions of mediation: "I want to make readers aware that maps [see map, mapping], like speeches and paintings, are authored collections of information and also are subject to distortions arising from ignorance, greed, ideological blindness, or malice" (Mark Monmonier, How to Lie with Maps). See also frame.