It's the minimum amount a family needs to earn in order to live at a basic, no-frills level. In other words: pay the rent and utilities, buy groceries, pay for childcare, etc.
A Basic Family Budget calculator is an important tool in determining if a family lives in poverty, because the system currently in place to do that is completely outdated.
Federal poverty guidelines, which dictate whether a family is eligible to receive assistance such as Medicaid and Food Stamps, are tied to a formula that was created in the 1960s. It was based on what the typical family spent on groceries because that was a family's biggest expense at the time. Today, necessities like housing, childcare and health care take up a far greater share of most family incomes than groceries. Not only do the guidelines not take these changes into account, they do not take into account regional differences in the cost of living.
Because the federal guidelines are so inaccurate, families are generally considered low-income when they earn up to twice (or 200 percent) the poverty level. This makes up for some shortfalls in the guidelines, but they are still nowhere near as accurate as a Basic Family Budget.