Janet was surprised to find out that her dentist, Dr. Herring, was good friends with her tennis partner, Sally. Janet met Sally years ago in graduate school, while Dr. Herring knows Sally from church. The nature of each one's relationship to Sally is what sociologists call a(n)

Tie.

Explanation:

In a social relationship strata, a tie refers to the connection one has with the friends or acquaintances of a friend. In other words, this form of relationship is formed with a mutual friend.

In the given condition, Janet knows Dr. Herring as a doctor-patient relationship whereas Janet and Sally are friends from school. So, the relationship of Janet, Sally, and Dr. Herring is what sociologists call a tie, where all individuals know each other but from different angles.