A cloud ledger is the record of balances and money movements for a new card or account, kept in a modern cloud system, separate from the bank's old core banking system. A ledger is a book of accounts. It lists every amount that comes in or goes out, against the right account.
Here is why banks use one. A bank's core banking system may be thirty years old. Changing it is slow and risky, because every account in the bank depends on it. So when the bank wants to launch a new credit card, it launches the card on a card issuing platform that comes with its own cloud ledger. The old core is not changed at all.
Say a customer gets the new card with a limit of ₹1 lakh. The cloud ledger opens a record for the card, with a balance of ₹0. She books a train ticket on IRCTC for ₹6,500. The ledger records ₹6,500 spent, and ₹93,500 still available. She repays ₹6,500 next month. The ledger records the repayment, and the full ₹1 lakh is available again.
A well-built ledger follows two rules. First, it records every amount twice: once as money leaving one account, and once as money arriving in another account. This is called double-entry bookkeeping. Because every amount is recorded on both sides, the totals must always match. Second, it never edits or deletes an old entry. If a mistake is made, the ledger adds a new entry that reverses it. So the full history is always available.
The bank's official books still need the totals from the new card. So the cloud ledger regularly sends summary figures to the old core. Every day, data reconciliation software checks that the two systems agree.
Over time, the bank can move more products and accounts onto the cloud ledger, a few at a time, until the old core is no longer needed. This is one common way of doing core banking modernisation. Fintech companies and neobanks also use cloud ledgers to keep their customers' balances.