Entitativity

Entitativity, in social science, is the perception of a group as a single entity (an entitative group), distinct from its individual members. Operationally, entitativity can also be defined as perceiving a collection of social targets (e.g., individuals) as possessing unity and coherence (e.g., a group). Entitativity is highest for intimacy groups, such as the family, lower for task groups, lower yet for social categories (e.g., people of the same religion), and lowest for transitory groups, such as people waiting at the same bus stop (Lickel et al., 2000).
Donald T. Campbell (1958) coined the term "entitativity" in order to explain why some groups are considered real groups while others are thought to be mere aggregates of individuals. He suggested that people rely on certain perceptual cues as they intuitively determine which aggregations of individuals are groups, and which are not (e.g. Spectators at a football game may seem like a disorganized collection of people, but when they shout the same cheers or express similar emotions, this gives them entitativity)(Forsyth, 2010). 
Additionally, Campbell (1958) emphasized three cues that individuals can use to make judgments regarding entitativity: "common fate" (the extent to which individuals in the aggregate seem to experience interrelated outcomes), "similarity" (the extent to which the individuals display the same behaviors or resemble one another), and "proximity" (the distance between individuals in the aggregate). 
To illustrate how we make those judgments, consider the example of people sharing a table at a library. They could be friends who are studying together, or they may also be strangers happening to share the same table. If you're wondering whether this is an actual group, you would examine their common fate, similarity, and proximity. Common fate may be something like the group all getting up and leaving together while talking or laughing amongst themselves. Similarity could be as simple as noticing that they are all using the same textbooks or notes, or that they happen to be wearing the same t-shirts to organizations (i.e., fraternity, university group). Finally, their physical proximity to one another (i.e., moving to sit closer) would be the final characteristic to judge that you are witnessing individuals with entitativity (Forsyth, 2010). 
There are two proposed antecedents for the entitativity perception (Ip, Chiu, & Wan, 2006):