Household

Definition

A household includes all the people who occupy a housing unit (such as a house or apartment) as their usual place of residence.

A household includes the related family members and all the unrelated people, if any, such as lodgers, foster children, wards, or employees who share the housing unit. A person living alone in a housing unit, or a group of unrelated people sharing a housing unit such as partners or roomers, is also counted as a household. The count of households excludes group quarters. There are two major categories of households, "family" and "nonfamily."

Household is a standard item in Census Bureau population tables. source

It’s physical building or apartment people live in. 4 individual single tax filing roommates count as a household.