A checkbook is the US spelling of chequebook: a pad of blank checks issued by a bank for a checking account. In bookkeeping the word also covers the record kept with it, the check stubs or register in which the holder notes each check written, each deposit made and the resulting balance.
The checkbook register as a record
For a household or very small business, the checkbook register is often the only cash record. Each entry shows the date, check number, payee and amount, and deposits are added. Keeping a running balance tells the holder how much money is available after allowing for checks that have been written but not yet presented, so the register works like a miniature Cash account.
The register balance and the bank's balance rarely match on any given day. Checks already deducted in the register may still be outstanding checks, deposits may not yet have been credited, and the bank may have deducted fees or added interest that the holder has not recorded. Comparing the two each month is a simple form of bank reconciliation, sometimes called balancing the checkbook.
Larger businesses no longer rely on paper registers. Their accounting software records every check in the cash disbursements module and the general ledger, but the logic is the same: recorded cash, less items not yet cleared, should agree with the bank's figure.