Household Income in the USA:  Link  Wikipedia

 
Household income is a measure commonly used by the United States government and private institutions, that counts the income of all residents over the age of 18 in each household, including not only all wages and salaries, but such items as unemployment insurance, disability payments, child support payments (not removing child support from wages and salaried yet counting it as overall income actually results in this money counting toward two households, artificially inflating the income between the two households), regular rental receipts, as well as any personal business, investment, or other kinds of income received routinely.[1] The residents of the household do not have to be related to the head of the household for their earnings to be considered part of the household's income.[2]
 
That the size of a household is not commonly taken into account in such measures may distort any analysis of fluctuations within or among the household income categories, and may render direct comparisons between quintiles difficult or even impossible. [3]
 
The 2006 economic survey also found that households in the top two income quintiles, those with an annual household income exceeding $60,000, had a median of two income earners while those in the lower quintiles (2nd and middle quintile) had median of only one income earner per household.