The available balance is the money available to spend in your Pleo wallet.
Compared to the current balance, the available balance is net of any pending transactions* that have not yet been settled with the merchant, where you recently have made a purchase.
If you have no pending transactions, your available balance will be the same as your current balance.
*Pending transactions: Sometimes it can take a few days for a merchant to complete the transaction; in this case purchases will appear as pending until the transaction is completed. In Pleo, we show you the pending transactions in your Expenses feed as we believe it can help you keep track of any upcoming transactions on your account.