Household

The household is the basic unit of analysis in many microeconomic and government models. The term refers to all individuals who live in the same dwelling.

Most economic models do not address whether the members of a household are a family in the traditional sense. Government and policy discussions often treat the terms household and family as synonymous, especially in western societies where the nuclear family has become the most common family structure. In reality, there is not always a one-to-one relationship between households and families.

Government definitions
For statistical purposes in the United Kingdom, a household is defined as "one person or a group of people who have the accommodation as their only or main residence and for a group, either share at least one meal a day or share the living accommodation, that is, a living room or sitting room" National Statistics.

The United States Census definition similarly turns on "separate living quarters", i.e. "those in which the occupants live and eat separately from any other persons in the building". A householder in the U.S. census is the "person (or one of the people) in whose name the housing unit is owned or rented (maintained);" if no person qualifies, any adult resident of a housing unit is a householder. The U.S. government formerly used the term head of the household and head of the family to describe householders; beginning in 1980, these terms were officially dropped from the census and replaced with householder.

The official definition from http://quickfacts.census.gov/qfd/meta/long_71061.htm is much more understandable and clearer than the mess above:

"A household includes all the persons who occupy a housing unit. A housing unit is a house, an apartment, a mobile home, a group of rooms, or a single room that is occupied (or if vacant, is intended for occupancy) as separate living quarters. Separate living quarters are those in which the occupants live and eat separately from any other persons in the building and which have direct access from the outside of the building or through a common hall. The occupants may be a single family, one person living alone, two or more families living together, or any other group of related or unrelated persons who share living arrangements. (People not living in households are classified as living in group quarters.)"

Economic theories
Most economic theories assume there is only one income stream to a household; this a useful simplification for modeling, but does not necessarily reflect reality. Some households now include multiple income-earning members.

Historical households
In feudal or aristocratic societies, a household may include servants or retainers, whether or not they are explicitly so named. Their roles may blur the line between a family member and an employee. In such cases, they ultimately derive their income from the household's principal income.