According to Wiki:
Cashier's cheques & banker's drafts
Cashier's cheques and banker's drafts are cheques issued against the funds of a financial institution rather than an individual account holder, decreasing the likelihood the cheque will bounce. Typically, cashier's cheques are used in the USA and banker's drafts are used in the UK. Though similar, they differ in their mechanics.
Cashier's cheques are issued by a bank cashier or head teller (or even by a major company). They are paid from the financial institution's funds immediately, without any clearing period. The financial institution then later takes the value of the cheque from the drawer. Cashier's cheques are perceived to be as good as cash but they are still a cheque, a misconception often exploited by scam artists.
The funds behind a banker's draft are paid when the draft is first drawn and are held by the issuing bank until the draft is cashed. Thus the funds of a banker's draft has been allocated and verified before the document is issued, providing a guarantee it will not be dishonoured due to insufficient funds. However, a lost or stolen banker's draft can be stopped like any other cheque so payment is not completely guaranteed.
[edit] Certified cheque
When a certified cheque is drawn, the bank operating the account verifies there are currently sufficient funds in the drawer's account to honour the cheque. A hole is punched through the MICR numbers so the certified cheque will not be processed as an ordinary cheque when it is deposited, and a bank official signs the cheque face to indicate it is certified. Although the face of the cheque is crowded, the back of the cheque is blank and the cheque can be deposited and routed through the banking system like an ordinary cheque.
While certified cheques guarantee there are sufficient funds to honour them at the time the cheque is drawn, they cannot guarantee there will be sufficient funds when the cheque is finally cleared for payment.
Link:
http://en.wikipedia.org/wiki/Cheque
