familiar stranger

Coined by American social psychologist Stanley Milgram in 1972.

familiar stranger (plural familiar strangers)

1. (social psychology) A stranger who is nonetheless recognized by another from regularly sharing a common physical space such as a street or bus stop, but with whom one does not interact.
   • 2018, Davide Spallazzo, Ilaria Mariani, Location-Based Mobile Games: Design Perspectives, Springer, →ISBN, page 39:

     The familiar stranger is someone we meet every morning at the bus stop or at the campus, but we have never talked with.

• familiar stranger on Wikipedia.Wikipedia