A blacklist is a subjective measure that a blockchain node can put into effect to block itself from putting into a block any transactions that were authorized by a defined list of blocked authors (accounts), or any transactions that interact with a defined list of contracts. Each node can specify their own blacklist, and these are not publicly viewable. If a node has blacklisted an author/contract, it will still accept the transaction as valid if another Block Producer places the transaction into a block. To ensure that an account or contract is fully blocked, all Block Producers will need to have the blocked account/contract on their blacklist at all times. Whitelist takes precedence over blacklist. Watch our video explanation.