What is actually meant by Block Height?
Any Bitcoin miner who successfully hashed a block header valued below the target threshold can add the entire block height to the block chain. This of course relies on the block standing as valid.
These blocks are usually addressed by their block height. Block height is defined by the number of blocks between a specific block and the first Bitcoin block. This original block is often referred to as Block 0, or more commonly as the Genesis Block.
With Bitcoin, this initial block is called Block 2016.
Identical Block Height
Multiple blocks can have the same block height. This is commonly experienced when two or more miners create a block at about the same time. This creates a visible fork in the blockchain.
If the miners produce simultaneous blocks at the end of the blockchain, each node individually selects which block to accept. The nodes usually use the first block they see.
Finally, a miner produces another block that is bound to only one of the competing blocks with simultaneous mining. This makes one side of the fork stronger than the other.
Assuming a branch contains only valid blocks, usually the most difficult chain is followed and rebuilt. Obsolete blocks belonging to shorter forks are then discarded.
Long-term forks are possible when different miners are working against each other. An example would be some miners working to lengthen the blockchain, while others attempt a majority attack against transaction history.
Since several blocks can have the same height the block height should not be used as a unique identifier. Instead, blocks are normally referenced by the hash of their header. This is often displayed in reverse byte order and hexadecimal.