Final answer:
A budget deficit occurs when the amount available for obligation is a negative number, and the government needs to borrow funds to cover the deficit.
Step-by-step explanation:
When the amount available for obligation is a negative number, it is referred to as a budget deficit. A budget deficit occurs when a government spends more money than it receives in taxes, causing a negative balance. This deficit then needs to be covered by borrowing funds, making the government a demander of financial capital.