Fault means being responsible for something that went wrong. When someone is at fault for breaking a window, they're the one who caused it to break. In a car accident, police determine which driver was at fault by figuring out who broke the traffic rules or made the mistake that caused the crash.

In sports, a fault is a specific kind of mistake that breaks the rules. In tennis, if you serve and the ball doesn't land in the correct box, that's a fault. In volleyball, touching the net is a fault. Each sport has its own particular faults.

People also use fault to talk about flaws or imperfections in someone's character or in how something is made. If your friend is always late, you might say tardiness is one of their faults. If a new phone keeps freezing, that's a fault in its design.

In geology, a fault is a crack in the Earth's crust where two pieces of rock move against each other. When these huge rock formations shift suddenly, they cause earthquakes. California's San Andreas Fault is one of the world's most famous geological faults.

The word appears in useful phrases too: finding fault means constantly pointing out flaws, while saying something happened through no fault of her own means she wasn't responsible for what happened.