To be mistaken means to be wrong about something, usually because you misunderstood the facts or made an error in judgment. When you're mistaken, you believed something was true that turned out not to be.

If you were certain today was Friday but it's actually Thursday, you were mistaken about what day it was. If you thought your friend was angry at you but they were just tired, you were mistaken about their feelings. Being mistaken is different from lying: when you're mistaken, you honestly believed what you said was true.

The word comes from the verb mistake, which means to misunderstand or misidentify something. You might mistake one twin for another, or mistake salt for sugar when baking (which would make some unpleasant cookies!).

Everyone gets things wrong sometimes. A scientist might be mistaken about a hypothesis and need to revise their theory. A witness might be mistaken about what they saw. When you realize you were mistaken, it's helpful to admit it and correct your understanding.