Household nicknames are often used to refer to family members in a loving and endearing way. 'POPPA' is a five-letter nickname for father, 'MAMA' is a four-letter nickname for mother, and 'SIS' is a three-letter nickname for sister. These terms are often used by children to refer to their parents and siblings, and can also be used by adults to refer to their own parents and siblings in a more informal setting.