A liar is someone who deliberately says things that aren't true. When you make an honest mistake about a fact, you're not lying. You're only a liar if you know the truth but choose to say something false instead.

People lie for different reasons. Some lie to avoid getting in trouble: a student might lie about finishing their homework when they actually forgot. Others lie to make themselves seem more impressive, like claiming they scored five goals in soccer when they really scored one. Some people lie to hurt others or to get something they don't deserve.

The word liar is serious and harsh. Calling someone a liar is a major accusation because it attacks their honesty and character. Once people discover someone is a liar, they may stop believing anything that person says, even when they're telling the truth. This is one of the real costs of lying: you can lose people's trust, and trust can be very hard to rebuild.

Everyone tells small lies sometimes, like saying “I'm fine” when you're actually sad. But a liar is someone who lies regularly or tells significant lies. The difference between someone who occasionally lies and a liar is how often they lie and how serious their lies are.