Sonia is like a really big piggy bank that the government uses to save money. It's a special kind of piggy bank that grown-ups use to keep track of how much it costs to borrow money. Think of it like when you borrow a toy from a friend, your friend might want you to give them back something extra like a piece of candy or share another toy with them. When the government wants to borrow money, they need to pay extra to the people who lend them the money (called investors). Sonia helps figure out how much extra they have to pay. It's an important tool to help make sure the government has enough money to pay for things like schools, hospitals, and roads.