Explain · Like I'm five version
The national debt in terms of a household overdraft
The national debt is just like your family asking to borrow extra pocket money from the shopkeeper.
Imagine your parents go to the corner shop for milk and bread, but they do not have enough pennies in their piggy bank. The shopkeeper says they can take the milk today, as long as they promise to pay him back later with a little bit extra. This is how the country gets its money when it needs to build new schools or fix the bumpy roads. We call this debt, and it keeps growing whenever the government spends more gold than it earns from our taxes.
Your parents have to be careful not to borrow too much, or the shopkeeper might get worried and stop being so kind. They try to pay him back slowly, bit by bit, by putting some of their own money into his jar every month. It is a bit like a big, never-ending game of pretend where everyone trusts each other to eventually put the coins back. If they spend too much on sweets and toys, there is less money left over to pay for the important things we really need.
Sometimes, the shopkeeper asks for a small fee for letting us keep his money for a long time. It is a bit like a tiny extra tax for the privilege of using someone else's piggy bank while we wait for our next pocket money. We keep paying this fee as long as we keep the debt, which makes the total amount we owe get even bigger. It is a very busy, serious job keeping all those shiny coins in the right places.
Where the analogy breaks downA country can print its own money and does not have to retire, so it can stay in debt forever unlike a person.