A certified check or certified cheque is a form of cheque for which the bank verifies that sufficient funds exist in the account to cover the cheque, and so certifies, at the time the cheque is written. Those funds are then set aside in the bank's internal account until the cheque is cashed or returned by the payee. Thus, a certified cheque cannot be stopped (can't "bounce"), and, in this manner, its liquidity is similar to cash, barring bank failure or illegal act (such as the funds being based on a fraudulent loan, at which point the cheque will be disavowed).
In some countries, e.g. Germany, it is illegal for a regular bank to certify checks. This regulation is supposed to prevent certified cheques from becoming a universal substitute for cash, which is considered the only legal tender. The Deutsche Bundesbank (Federal Bank) is the only financial institution authorized to issue certified checks.
Because of the liquidity and certainty of payment of a certified cheque, it is sometimes considered equivalent to cash, such as in the regulation of credit for casino gaming in Macau, where the law explicitly states that if a casino patron obtains casino chips and pays with a certified cheque, the transaction is not regarded as credit for gaming (see Law 5/2004, art. 2).
It is possible to counterfeit or forge a certified cheque, in which case it is not binding on the bank and is worthless. See entry on cashier's check for an exploration of associated risks.