Reorg

Reorg is the everyday shorthand for a chain reorganization — the moment a blockchain drops one branch of recent blocks in favour of another. For users the effect is visible rather than theoretical: a transaction that showed two confirmations can fall back to zero, an exchange deposit can be un-credited and then credited again, and a block explorer may stop displaying a block it showed minutes earlier. Most reorgs are one block deep and resolve in seconds. Exchanges set confirmation thresholds per network based on how often and how deeply that chain reorgs, which is why a deposit on one chain clears in a minute while another takes an hour. Treat a payment as final only after the confirmations the receiving service requires.