Final answer:
The phenomenon described is known as the feminization of poverty. It refers to the increase in the number and percentage of women among the nation's poor.
Step-by-step explanation:
The phenomenon described, where single-parent households headed by women are more likely to live in poverty compared to those headed by men, is known as the feminization of poverty. This term refers to the increase in the number and percentage of women among the nation's poor due to factors such as the rising number of female-headed households and the increased tendency for these single mothers and their children to fall below the poverty line.