Reorg

A blockchain reorganisation, in which a recently-confirmed block (or a short chain of blocks) is replaced by a competing block that the network accepts as canonical instead. Transactions in the orphaned block are returned to the mempool. 1-block reorgs happen frequently on most chains (missed slots, network delays); deeper reorgs are rare and signal stress. Finality mechanisms make reorgs past a certain depth essentially impossible without slashing-level economic loss.