In the original Russian, Остранение [ostranenie, also translated enstrangement, making strange, strangefication).
The soviet literary theorist Viktor Shklovsky used this word to refer to the power of art to make us perceive familiar things in a fresh way, or to actually see them again. Shklovsky thought all the best art does this, but some members of the avant garde considered this to be a principle of progressive art battling the false consciousness of capitalist consumer culture, returning us to a truer understanding of aspects of our lives that we have stopped noticing because of repetition and cultural and social normalization.
When we see things over and over again our perception becomes stale and automatic. Art returns us to a mindful awareness of things. Defamiliarization attempts to make what has become too familiar to us through overexposure seem “strange” to us again. Instead of merely registering things in an almost subconscious process of recognition/acceptance, we once again see and think about them, and may thus come to re-evaluate them.
Some remix art seems to have this as its intention, or at least its effect. Dadaist photomontage, the works of surrealism, pop art, appropriation art could all be seen as engaging in defamiliarization. It could be argued that a genre like the YouTube Poop is pursuing the project of defamiliarization with our mass media.
See also alienation effect.