Context collapse is a concept used by those academics writing about the effects of social media. It refers to the infinite audiences possible online as opposed to the limited groups a person can normally interact with in face-to-face circumstances. In bounded interactions, people adjust their tone and presentation to fit the social context. In a situation of context collapse, this becomes impossible.
In social media, face work does not have the same currency or value because we don't see the expressions of those with whom we are communicating. Further, there is context collapse, or homogenization of context, because all of the micro-calculations we used to make by evaluating a situation are gone, removed and collapsed in social media.