A group of Ravens is an "unkindness" of Ravens

"Covered in jet-black feathers, ravens are a mysteriously interesting species of birds, having high levels of intelligence and taking up a buoyant and graceful flight. But, perhaps due to their absurd appearance, the birds are considered evil and harsh, and hence, referred to as an ‘Unkindness’ together in a group."

https://www.birdwatchingusa.org/what-is-a-group-of-ravens-called