A voided check is a check that the writer wrote and then later canceled. The writer could have canceled the check because there was a mistake on it, or they may have issued the check by mistake.
Usually, a voided check is perforated with a "void" stamp to show that it cannot be cashed. It is advisable to destroy a voided check completely so that a person cannot take it to the bank. If a bank has the check, it is necessary to contact them so that the bank does not try to cash the check. Voided checks may also be created to prevent fraud.