(This is the sum of all the transactions after the latest statement date which are authorised by you but are yet to be billed to your account. In case you have availed Cash-on-Call, it also includes the Cash-on-Call principal amount which is outstanding on your card account.)
Sometimes it happens that merchants submit all transactions in bulk. So although the authorization has passed through and the amount blocked from your credit limit. The transaction is yet to be completed and hence not showing up on your bill.
Once the merchant completes the formalities by submitting your counter signed authorization slip, the item will appear in your credit card statement in the next billing cycle.
Total outstanding amount is the amount that is yet to be claimed by the merchant. Once the merchant claims the purchase amount paid by the credit card, then only it will come under unbilled transactions.