Usually, in an exchange, you can have several accounts with different usages (Classical, trading, margin trading, futureā€¦) and then, you have a balance for each currency.

A balance is not simply the amount you have, it could be more complicated and have the following values :

Field Description
currency Currency
total Returns the total amount of the currency in this balance
available Returns the amount of the currency in this balance that is available to trade
frozen Returns the frozen amount of the currency in this balance that is locked in trading
loaned Returns the loaned amount of the total currency in this balance that will be returned
borrowed Returns the borrowed amount of the available currency in this balance that must be repaid
withdrawing Returns the amount of the currency in this balance that is locked in withdrawal
depositing Returns the amount of the currency in this balance that is locked in deposit