OP_RETURN

OP_RETURN is a Bitcoin script opcode that allows small amounts of arbitrary data to be embedded in a transaction. Outputs using OP_RETURN are provably unspendable, meaning the bitcoin associated with them cannot be spent. A famous early example of embedded data is found in the first Bitcoin block (the genesis block), which contains the message “The Times 03/Jan/2009 Chancellor on brink of second bailout for banks,” serving as a timestamp and commentary.