English has a very unusual habit of having specialized words to mean "group" when describing certain animals. We say a "litter" (of puppies or kittens) when talking about a group of newly born animals. This is a different meaning than the word "litter" that means "trash". In this case, a litter is used to describe a set of animal babies that are born at the same time. We sometimes say something is "the pick of the litter" which means the nicest puppy of all the puppies, or the best choice option in a set of options. Note that "litter" is only used for animals. If a woman had triplets (three babies at once), it would be rude to say she had a litter of children because that makes her seem like an animal. When we talk about older adult animals, there are more specialized words to mean "a group" of animals. We say a pack of dogs, or a gaggle of geese, or a pod of whales, or a murder of crows. Some of these are very rarely used, and only known by language enthusiasts. Here is a list of these unusual terms: http://rinkworks.com/words/collective.shtml

A "litter" is just another fancy english word meaning "group", all it means is for a group of puppies to be born

I have just find about puppies too.