tombstones

Tombstones are special markers used in blockchain technology, like those in cryptocurrencies such as Bitcoin. They are permanent files that indicate a specific transaction or block has been invalidated or replaced—often after a transaction is reversed or a chain is reorganized. Think of them as digital "footnotes" or "warnings" that help maintain the integrity and history of the blockchain by marking which data is no longer active or correct. Tombstones ensure the network’s consistency and trustworthiness, making it clear which parts of the blockchain are current and valid.