Debt of developing countries means money that they have borrowed from other countries or organizations and have to pay back. It's like when you borrow money from a friend and have to pay it back - except that developing countries borrow from big organizations, like the World Bank, or from other countries like the United States or China. Developing countries often get these loans so that they can build things like roads, schools, and hospitals and help people there get a better life. Unfortunately, sometimes it can be hard for developing countries to pay back the money they borrowed, which means they can get stuck in debt for a long time.