A genesis block is the first block ever mined or created in a blockchain network. It symbolizes the beginning of distributed ledger technology, recording the first-ever transaction to take place on the network.
The genesis block is called Block 0 or Block 1 and is hardcoded into the blockchain application software. Every other block created within the blockchain can trace back the origin of the network to this first block owing to the transparent nature of the technology.
For instance, the Bitcoin genesis block was released on 3 January 2009 and contained the first 50 bitcoins created. Bitcoin's creator Satoshi Nakamoto had added a message in the genesis block of Bitcoin, stating, "The Times 03/Jan/2009 Chancellor on the brink of second bailout for banks".
