NOT "invented by internet forum users." It's a phrase that's been in use for a couple hundred years. It means alike with a connotation of close. Like BFFs that have exactly the same tastes and wear the same clothes.
Hannah darling you are my other pea, we share the same pod!! I love you so much darling and I'm so glad I met you!! your the closest friend I've had in a long time and one that I never wanna loose you!!!!!