Chain Reorganization

A chain reorganization, commonly shortened to reorg, is when nodes discard blocks they previously treated as the tip of the chain and adopt a different branch that the consensus rules judge to be stronger. It is a normal part of how networks converge: two block producers publish at once, the network briefly disagrees, and the losing branch is dropped. Transactions in discarded blocks are not destroyed — most return to the mempool and are mined again — but they lose their confirmations, and their ordering or inclusion can change. Deep reorganizations spanning many blocks are rare on large networks and usually signal a serious problem such as a client bug or concentrated block production. Confirmation requirements exist precisely to absorb this risk.