Originating from Neopets.com, a "neotwin" is a relationshpi between two good friends. So good they have decided they're like twins. Since they're not biological twins, but they seem so similar, they decided to call it "neo"twins to give honour to the place where they met, Neopets.com!
You know chocolateluvr? She's the best neotwin in the world. One day we must go to Disneyland together.