Short-lived immunity acquired from mor to foetus across placenta or through mor's milk to infant is categorised as 

Immunity is transferred across placenta from mother to the foetus or through breast milk of mother to the infant passively in the form of readymade antibodies which can provide protection against bacteria and viruses until the baby can synthesize its own antibodies. Therefore, it is a short-lived immunity. World Heath Organization recommends that breast feeding must be given for the first two years of life to provide immunity to the child. This kind of immunity which is transferred directly in the form of readymade antibodies is called as passive immunity.
So, the correct answer is 'Passive immunity'