The Singer-Prebisch thesis is an economic theory that suggests a long-term decline in the terms of trade for developing countries compared to developed nations. This means that as developing countries export raw materials, they receive less value in return for their goods than what developed countries earn from their manufactured products. This thesis highlights the structural inequalities in global trade, arguing that developing nations often remain dependent on exporting primary commodities. As a result, they struggle to achieve sustainable economic growth and development, leading to a cycle of poverty and underdevelopment.