Definition
Block height identifies a block’s position relative to the beginning of a chain. In Bitcoin and many other networks, the genesis block has height zero and its immediate successor has height one. Height measures sequence rather than elapsed time, transaction count or the size of the stored blockchain.
How It Is Used
Applications may use height to locate records, schedule protocol events or express how far a node has synchronized. If a transaction is included at height 100 and the current tip is 102, it has three confirmations under the common convention that counts its own block. A protocol may use other concepts, such as slots and epochs, which should not automatically be treated as block heights.
Key Considerations
During a fork, different blocks can exist at the same height. Height alone therefore does not uniquely identify a block; a block hash and network context are also needed. A chain reorganization can replace the block at a given height. Comparing heights across different blockchains does not measure their age or security, because block-production rules and timing differ.