A control account is summary level account in the general ledger. The control account contain aggregated totals for transaction that are individually stored in the subsidiary ledger account. Control account are most commonly used for accounts receivable and account payable since these areas contains large volume of transactions, so need to be separated into subsidiary ledger rather than cluttering up general ledger with too much detailed information.
The balance in the control account should match the total for the related subsidiary ledger. If the balance does not match, it is possible that a journal entry was made to control account that was not also made in the subsidiary ledger.