Block height is the number of blocks in the chain between any block and the first block (genesis block or block 0) in the blockchain.
Every block in the blockchain has an associated block height value. The first block in the blockchain, known as the genesis block, has a block height of zero, reflecting the fact that there are no blocks before it in the chain.
Block height is an important measure of the rate at which new blocks are being added to the blockchain. It is also used as an identifier for each individual block.
However, in some circumstances, two blocks might have the same block height. This occurs if the same problem is solved simultaneously by more than one miner which would cause two blocks to be created with the same block height. This may precipitate a fork, or it may result in a block being orphaned. Duplicate blocks cannot appear on any given blockchain.
Block height is one of the key pieces of information displayed on block explorers. It is also one of the most useful pieces of information to find details of specific blocks or transactions.