Final answer:
In blockchain, a hash is an encrypted code representing the data within a block, created by a hashing algorithm. It ensures the data's integrity and facilitates its verification without revealing the actual data.
Step-by-step explanation:
A "Hash" in blockchain technology refers to option B: "It is basically an encrypted code calculated when the data is added to the block." When a transaction is made on a blockchain, the details of the transaction are run through a hashing algorithm. This process generates a unique alphanumeric string of fixed length, regardless of the size of the transaction data. This hash acts like a digital fingerprint, uniquely representing the data within a block. If even a single character in the data changes, a completely different hash will be produced, making it an effective way to ensure data integrity.