An accident is something that happens unexpectedly and unintentionally, usually causing damage, injury, or unwanted results. When you knock over a glass of milk while reaching for the salt, that's an accident: you didn't mean to do it, and you certainly didn't plan it. When two cars collide on an icy road, that's a car accident: neither driver intended for it to happen.

The key element of an accident is the lack of intention. If your little brother deliberately pushes your science project off the table, that's not an accident, even if he claims it was. But if he trips over his shoelaces and bumps into the table, knocking your project to the floor, that genuinely is an accident.

People often say “I'm sorry, it was an accident” to explain they didn't mean to cause harm. This matters because we usually treat accidents differently from deliberate actions. A friend who accidentally steps on your toe deserves understanding, while someone who does it on purpose deserves a different response.

Some accidents are minor, like misspelling a word or leaving your homework at home. Others are serious, like workplace accidents or traffic accidents that injure people. That's why we have safety rules: wearing bike helmets, using crosswalks, and following laboratory procedures all help prevent accidents before they happen.