"Pseudo" means "Fake", while a "Jinchuriki" is those with a Tailed Beast inside of them. In Naruto, a Pseudo-Jinchuriki means someone who has a portion of a Tailed Beast's chakra sealed in them, but not the beast itself. For example, the Gold and Silver Brothers possessed a portion of the Nine-Tails' chakra from eating its flesh, but didn't have the beast sealed in them.