Actualization is the coming forth of the virtual into the actual. In Difference & Repetition, Deleuze prefers the term actualization to representation because the latter relies on a binary system of thought he critiqued throughout his career. Actualization is related to expression, stemming from his persistent interest in the world as itself an expressive and immanent entity. The world consist of neither representations, nor is it directly inhabited without mediation.
In A Thousand Plateaus, Deleuze and Guattari defines actualization as occurring specifically in the plane of immanence. The plane of immanence is constituted at the interface of the virtual and its actualization, which is simultaneously the point at which the actual object folds back into the virtual images that support it.
Every experienced moment that presents itself as an actualization is brought to a plane by moments of the past, and its significance folds back into the virtual structure of the past which sustains it. A tree, for instance, is not simply a punctuation in the field of the visual. As Todd May writes, “There is no present that does not actualize the past. It is all of the past that is actualized at every moment. The past that is actualized exists.” Actualization is the past as it is lived throughout an unfolding present that folds back into the past. There are no cuts with Deleuze, as if the present is cut from the past, only ongoing continuities, flows, and unfoldings. Memories are a fold in this virtual fabric: “degrees or modes of actualization which are spread out between two extremes of the actual and the virtual: the actual and its virtual on the small circuit, expanding virtualities in the deep circuit.” The virtual and the actual are entwined in one another.