An account is matchable, i.e. it handles both debit and credit transactions. Usually, customer and supplier controlling accounts are defined as matchable (see Account Inquiry function).
An account can be declared as reconciled which permits focusing on specific transactions. A bank account is usually declared reconciled: i.e. when the bank statement is received, the transactions described on the bank statement are verified. The transactions that are not reconciled are the transactions that have not yet been process by the bank (a check that has been issued but not cashed, for example).