A surplus is an amount of something that's left over after you've used what you need. If your school cafeteria orders 500 lunch trays but only 450 students show up, there's a surplus of 50 trays. If a farmer grows more corn than she can sell, she has a surplus of corn.

The word appears often in discussions about money and budgets. When a government collects more tax money than it spends in a year, that's called a budget surplus. Families can have surpluses too: if your parents budget $100 for groceries but only spend $85, they have a $15 surplus to save or spend on something else.

Surplus is the opposite of shortage or deficit. A shortage means you don't have enough of something you need. A surplus means you have extra. Countries sometimes donate surplus food to places that need it, or sell surplus military equipment they no longer use.

In everyday conversation, you might hear someone say “I have a surplus of ideas” for the science fair, meaning they have more good ideas than they can possibly use. The word can carry a positive feeling: having a surplus usually means you planned well or were productive enough to create more than the minimum required.