mistake
Something done wrong by accident, not on purpose.
To make a mistake means to do something wrong or incorrect, usually by accident rather than on purpose. When you spell a word wrong on your homework, add instead of subtract on a math problem, or forget to feed the dog, you've made a mistake. Everyone makes mistakes: they're a normal part of learning and living.
The key difference between a mistake and cheating or lying is intention. Mistakes happen when you're trying to do the right thing but get it wrong somehow. You might make a mistake because you misunderstood the instructions, moved too quickly, or simply didn't know any better. A basketball player who passes to the wrong teammate made a mistake, but they weren't trying to mess up the play.
Some mistakes are small and easy to fix, like putting salt in your tea instead of sugar. Others can be more serious, like hurting a friend's feelings without meaning to. Scientists and inventors make thousands of mistakes while working toward discoveries.
As a noun, a mistake is the thing that was done wrong (“That answer was a mistake”). As a verb, to mistake something can also mean to confuse it with something else (“I mistook her for her sister”).