Answer:
Collective noun
Step-by-step explanation:
Collective nouns are nouns that are normally in its singular form but that refers to more than one person, animal, thing or concept considered as a single entity because they share one or more characteristic.
"Congregation" is an example of a collective noun because this noun it's singular but it refers to two or more persons organized for some specific purpose.
Some other examples of collective nouns are team, class, herd, flock, gang, mob, group, and family.