A familiar stranger is an individual whom one frequently sees, usually but not always in the same setting, but with whom one does not interact. The relationship that exists between familiar strangers is a subject of interest in sociology because a relationship of sorts does exist even without interaction. A familiar stranger may be a classmate, someone seen often at the gym, someone who sits nearby on the subway, or any of many other repeatedly-seen people. The "relationship" between these strangers arises from the mutual decision not to interact in spite of regularly being near each other. Familiar strangers are often closely bound to one's perception of a particular place more than they are defined by the particular characteristics of people.
The non-interaction aspect of the familiar stranger relationship may be terminated if the strangers encounter each other away from their normal meeting places. Individuals who see each other at the laundromat on a regular basis, for instance, are likely to interact if they encounter each other while on vacation somewhere far from home. Additionally, disasters or other extraordinary circumstances may prompt one to interact with a familiar stranger. The familiarity tends to provide some level of support and comfort in unsettling or frightening circumstances.
It is quite common for one to assign a fictional back story and nickname to a familiar stranger based on appearance and behavior. Doing so tends to make one feel somewhat closer to the familiar stranger and has a personalizing effect. If familiar strangers do eventually meet, each may explain the details of the fictional personas that they applied to each other, often with the effect of great mutual amusement.
Familiar strangers are more common in some types of communities than in others. In particularly small groups, such as private schools, small businesses, and small, close-knit neighborhoods, it is relatively rare for the familiar stranger to remain a stranger for a long period of time. The small size of the community makes interaction quite likely and may also make aloofness and intentional avoidance of interaction somewhat rude. In such communities, it is possible to have some form of minor relationship with just about everyone, and the small size of the community makes some form of interaction almost inevitable.
In densely-populated urban areas, on the other hand, nearly everyone is likely a familiar stranger to someone else. The sheer number of people that one likely encounters on a day-to-day basis makes meaningful social interaction with each person nearly impossible. Attempting to initiate social connections in these densely-packed urban areas also can often be seen as irritating and rude.