A group of hens is called a run, a term borrowed from poultry-keeping vocabulary that actually refers to two related things: the group of hens themselves, and the fenced outdoor enclosure, the “chicken run”, where they’re kept and allowed to roam. Over time, the term for the space came to describe the birds that live in it too.
Hens are social, hierarchical animals that establish a well-documented pecking order within their group, a literal, observable ranking system that determines feeding priority and social standing. A run of hens isn’t a random gathering; it’s a structured little society with its own internal politics.
Bonus fact: hens can recognize and remember over a hundred individual faces, including other hens and the humans who care for them.
Hens are also grouped under the more general term brood, especially when referring to a mother hen with her chicks.
Related: Collective Nouns for Birds · What Is a Group of Hens Called?