"I have argued that most often in social sciences, 'social' designates a type of link: it's taken as the name of a specific domain, a sort of material like straw, mud, string, wood, or steel. In principle, you could walk into some imaginary supermarket and point at a shelf full of 'social ties,' whereas other aisles would be stocked with 'material,' 'biological,' 'psychological,' and 'economical' connections. For ANT … the definition of the term is different: it doesn't designate a domain of reality or some particular item, but rather is the name of a movement, a displacement, a transformation, a translation, an enrollment. It is an association between entities which are in no way recognizable as being social in the ordinary manner, except during the brief moment when they are reshuffled together.
To pursue the metaphor of the supermarket, we would call 'social' not any specific shelf or aisle, but the multiple modifications made throughout the whole place in the organization of all the goods — their packaging, their pricing, their labeling — because those minute shifts reveal to the observer which new combinations are explored and which paths will be taken (what later will be defined as a 'network')."
— Bruno Latour, Reassembling the Social, 64-65
(Lots more Latour here, bien sur.)