An expense is money that you spend to buy something or pay for a service. When your family pays for groceries, electricity, or a new pair of shoes, those are all expenses. Your school has expenses too: teacher salaries, textbooks, building maintenance, and cafeteria supplies all cost money.

The word often appears when people talk about managing money carefully. A business tracks its expenses to make sure it's not spending more than it earns. Your parents might create a budget that lists all their monthly expenses: rent or mortgage, car payments, insurance, food, and entertainment. When something is described as expensive, it means the cost is high compared to similar things.

People also use expense to describe non-monetary costs. You might say that winning the championship came at the expense of your free time, meaning you sacrificed leisure hours to practice. Or someone might succeed at the expense of their friendships, meaning they gained something but lost something else valuable in the process.

Understanding expenses helps people make smart choices about money. If you earn $20 from mowing lawns but your expenses for gas and equipment are $15, you've only really earned $5. The difference between what you earn and what you spend determines whether you're ahead or behind.