An outstanding check is a check that has been written by a company (and deducted from the appropriate general ledger cash account) but it has not yet cleared the bank account on which it is drawn. Hence, outstanding checks will mean that the balance in the bank account will be greater than the balance in the general ledger account (or in an individual's check register).
In the bank reconciliation process, the total amount of outstanding checks is subtracted from the ending balance on the bank statement when computing the adjusted balance per bank.
Checks that are outstanding for a long period of time are known as stale checks. In the U.S. outstanding checks are considered to be unclaimed property and the amounts must be turned over to a company's respective state after several years. Rather than allowing checks to become stale and then remitting the money to a state government, companies should contact the payee of any check that has been outstanding for several months.
The amount of outstanding checks is sometimes referred to as float.