Median Household Income for a household where householder has a high school diploma (but no college) is $55,810. 24.1% of ALL US households fall into this category.
It's probably a dated term from when men were the de facto "kings of the family". I'm surprised it's still used in census data, but it probably refers to the primary bread-winner, aka whoever makes the most money in the household.
Edit: It occurred to me afterwards they might just be referring to whoever has their name on the deed for the house.