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Original definition refers to a group of baby animals born to the same mom such as a litter of kittens or puppies.

New definition: people who share your birthday and therefore same astrological influences.
I just checked out my birth day online and found out that there's a ton of famous people who are my litter mates.

Because we share the same birthday, my best friend and I are litter mates.
by angeet June 04, 2010