According to the feline overlords of the internet, when you want to describe a group of cats, you call them a "herd" of cats. Because, let's be real, they're basically just a bunch of wild, fluffy animals running around and causing chaos.
Here are some more examples of collective nouns:
Remember, these are all real words, but only used by pretentious English majors and linguists. The rest of us just call them "a bunch of cats".