Social objects, for example in social interaction design or in the enterprise, are those things around which collaborations and networks form – online they might be such things as blogs, photos, Facebook postings or web clippings. These are at least ‘real’ objects in the sense that Winnicott used to distinguish object-usage from object-relating. Winnicott argued that in surviving its destruction by the subject as a basis for object-relating, the object is established as being ‘external’. But what makes these external objects social is the way they are taken up as the basis of reciprocity or mutuality in the manner of Freud’s third identification i.e. an identification formed not with some one or some way of thinking, but rather with a situation engendering a particular affective relation – with a situation that is symptomatic. The identification is with a way of being-in-relation-to-situation.
Jyri Engeström was at the epicentre of the use of this term, but he refers its meaning to the work of Karin D. Knorr Cetina, in particular her papers on “Sociality with Objects” and The Market as an Object of Attachment”. Karin argued that instrumental objects had to be distinguished from knowledge objects. Instrumental objects formed part of an increasingly mechanised and commoditised world that were experienced as complete in themselves, while knowledge objects were experienced as complex, question-generating, endlessly unfolding and incomplete. Unlike instrumental objects, which supported an action-oriented approach to the world of doing and accomplishing, knowledge objects supported a meaning-oriented approach of reflexive experiencing, feeling and remembering. Knowledge objects supported an object-centered sociality referred to by Jyri as a world of social objects.
In explaining the basis of knowledge objects aka social objects, Karin argued that the ‘real’ object came to serve as a knowledge object aka social object to the extent that it supported a being-in-relation, mutuality or reciprocity between individuals on the basis of enabling temporal synchronisation or on the basis of establishing a shared temporal immediacy – individuals able to collaborate around a shared task, or individuals able to be present to each other in some situation (in contrast to the more familiar spatial synchronisation and immediacy of a face-to-face meeting). Furthermore, to the extent that this mutuality was experienced, it was experienced as a ‘We’-ness embedding the individual in a larger context, but derived from the nature of the shared situation rather than from an institutional affiliation. And its efficacy in serving as a knowledge object aka social object depended on there being a fit between the nature of the object’s incompleteness and the individual’s own experience of lack – an identification between the individual’s lack and that of the object corresponding to the Lacanian i(a) – the imaginary form given to the subject’s relation to objet petit a aka lack.
The Kleinian object, then, is a way of speaking about the organisation of the individual’s primary process. With symbol formation, the ‘real’ object becomes established as external, its symbolisation becoming a knowledge object to the extent that the individual’s unconscious experience of the symbolisation is as being incomplete. In the ‘real’ object becoming a knowledge object aka social object, it becomes a Lacanian signifier that signifies an i(a) for the subject qua symptom to the extent that it becomes identified with the individual’s unconscious experience of lack. 
 The quote is from Winnicott, D. W. (1969). “The use of an object.” International Journal of Psychoanalysis 50: 711-716.
 Note the distinction here between symptom and sinthome. While ‘symptom’ is the Imaginary form given to a Symbolic lack made present by the subject’s relation to the Real i.e. Imagining the Real in the Symbolic, ‘sinthome’ is more akin to Symbolising the Real in the Imaginary – experiencing a limit to symbolisation itself as a way of ‘knowing’.