A bank draft (also called a banker's draft or cashier's check) is a check issued by the bank itself, guaranteeing payment. Unlike a personal check (which might bounce), a bank draft is backed by the bank's own funds — making it virtually as good as cash.
When you request a bank draft, the bank immediately debits your account for the draft amount plus a fee ($5-15 typically). The money is set aside by the bank. When the recipient deposits the draft, the bank honors it without question because the funds are already guaranteed.
Bank drafts are used for high-value transactions where the payee wants guaranteed payment — real estate purchases, vehicle sales, business transactions, and international payments. They are harder to forge than personal checks and carry the bank's reputation. However, beware of fake bank drafts — scammers create convincing forgeries.