What is litter a collective noun for?

"Litter" is a collective noun for a group of young animals, specifically the offspring of certain animals born at the same time, especially mammals.

Here are some examples:

* A litter of puppies

* A litter of kittens

* A litter of piglets

* A litter of rabbits

It's important to note that "litter" is not used for all animal offspring. For instance, you wouldn't say "a litter of baby birds" or "a litter of fish."