What term describes a large assembly of individuals who engage with one another according to loosely established norms?

Explanation

A craze (A) refers to a temporary trend. A group (B) usually implies a smaller number with stronger bonds. Contagion (C) relates to rapid spread, often of emotions or diseases. A collectivity (D) is a large number of people interacting based on loosely defined norms, making it the correct answer. A mob (E) suggests a disorderly crowd.